Patent Publication Number: US-10319505-B2

Title: Electro-magnetic flux valve

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Patent Application Ser. No. 62/295,410 entitled Electro-Magnetic Flux Valve and filed on Feb. 15, 2016, which is incorporated herein in its entirety. 
    
    
     BACKGROUND 
     Past concepts involving movable core material and unique coil driven core designs have been employed with limited success to design an economical low power solution for the control of passive Rare Earth Magnet flux in a magnetic power converter. Typically, the goal has been to develop a “solid state” switch with no moving parts that requires a minimal energy input for a wide control of device permeability defined as: 
     
       
         
           
             
               
                 
                   μ 
                   = 
                   
                     B 
                     H 
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     Where:
         μ=permeability of the core shunt   B=magnetic field flux density in gauss   H=magnetizing force in amperes/meter       

     Often, an external coil is used to control the flux density B through the core material of the switch device; however, this method has proven to have limited effectiveness due to the inductive reactance limiting the frequency of the input drive signal and the reactive power requirement. 
     SUMMARY OF THE PRESENT DISCLOSURE 
     An apparatus of the present disclosure  FIG. 1  has a magnet  13  surrounded by a ferromagnetic core  14  acting as a shunt to the magnetic flux field of the magnet  13 . The ferromagnetic core may be made of Permalloy steel laminations; however, it may be made of other types of materials in other embodiments. The ferromagnetic core shunt  14  of the present disclosure has two voids  12  and  15  on opposing sides of the magnet  13 , which allow a flux control coil  16  to pass through the core shunt  14  and around the magnet  13  thus forming two flux control elements adjacent to the magnet. The voids are configured such that the outer flux path  17  will saturate while the inner flux path  18  will provide a linear flux control proportional to the H field applied by the flux control coil. Note that the outer flux path is the outer portion of the core  14 . The flux control coil  16  produces a local magnetic field which circulates around each void  12  and  15  independently and moderates the local flux density around each void thus forming two flux field control elements to moderate the reluctance of the overall core shunt  14 . 
     When the Electro-Magnetic Flux Valve (EMFV) is placed in an external magnetic circuit  FIG. 4  the amount of flux control can be quantified from the voltage induced into the output coil  45  as the magnetic flux shifts back and forth. The standard equation for the transformer is based on Faraday&#39;s law and produces accurate results for the determination of EMFV flux control. 
     
       
         
           
             
               
                 
                   
                     B 
                     m 
                   
                   = 
                   
                     
                       
                         E 
                         s 
                       
                       × 
                       
                         10 
                         8 
                       
                     
                     
                       4.44 
                       ⁢ 
                       
                         fN 
                         s 
                       
                       ⁢ 
                       A 
                     
                   
                 
               
               
                 
                   Equation 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     Where:
         B m =magnetic field flux density in gauss   E S =voltage induced in the output coil in rms   f=the frequency of operation in Hertz   N S =the number of turns in the output coil   A=the cross sectional area of the output core  44  in square centimeters       

     The total amount of flux controlled by the EMFV is actually twice the value calculated by equation 2 due to the fact that the EMFV controls the flux in one direction. In  FIG. 6 , when the flux  61  shifts into the external magnetic circuit  62  the voltage in the output coil  66  swings to a positive peak value. In  FIG. 5 , when the flux  51  shifts out of the external magnetic circuit  52  and the magnetic flux  51  is again constrained by the EMFV, the voltage in the output coil  56  swings to a negative peak value. 
     The boost circuit  FIG. 9  used to drive the EMFV is unique in that the pulse and boost cycles are electrically isolated to support the recovery of a large part of the reactive power required to operate the EMFV. The isolated boost circuit also employs a bootstrap capacitor C 1  to establish a boost base threshold voltage level to maximize the energy transfer back into the D C Link (DCL) C 2  and the battery B 1 . 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure can be better understood with reference to the following drawings. The elements of the drawings are not necessarily to scale relative to each other, emphasis instead being placed upon clearly illustrating the principles of the disclosure. 
         FIG. 1  is an isometric view of the Electro-Magnetic Flux Valve (EMFV) according to an exemplary embodiment of the present disclosure. 
         FIG. 2  illustrates an induction curve and the Stoletov curve for M19 electrical steel. 
         FIG. 3  illustrates the induction curve and the Stoletov curve for Carp 49 electrical steel. 
         FIG. 4  is a plan view of the EMFV placed within an external magnetic circuit which includes an output coil to measure flux density according to an exemplary embodiment of the present disclosure. 
         FIG. 5  is a plan view of the EMFV, with the control elements at quiescence, showing the permanent magnet flux constrained within the EMFV shunt circuit. 
         FIG. 6  is a plan view of the EMFV, with the control elements energized, showing the permanent magnet flux shifted out of the EMFV shunt circuit into the external magnetic circuit. 
         FIG. 7  is an isometric view of the widened core version of the Electro-Magnetic Flux Valve (EMFV) according to an exemplary embodiment of the present disclosure. 
         FIG. 8  is an isometric view of the widened core version of the Electro-Magnetic Flux Valve (EMFV) placed in an external frame according to an exemplary embodiment of the present disclosure. 
         FIG. 9  is a simplified schematic diagram of the isolated boost circuit used to drive the EMFV according to an exemplary embodiment of the present disclosure operating in the Drive Cycle. 
         FIG. 10  is a simplified schematic diagram of the isolated boost circuit used to drive the EMFV according to an exemplary embodiment of the present disclosure operating in the Recovery Cycle. 
     
    
    
     DETAILED DESCRIPTION 
     The EMFV of the present disclosure of  FIG. 4  consists of a permanent magnet encircled by a low reluctance ferromagnetic shunt core  14  ( FIG. 1 ) composed of segments  41 ,  42 ,  46  and  47  that control the flux produced by the magnet  43 . Two of the shunt core segments,  46  and  47 , are configured to control a flux produced by the magnet  43 . When the flux control segments  41 ,  42 ,  46 , and  47  are electrically energized, their reluctance increases and the permanent magnet flux shifts from the shunt core to the external magnetic circuit core  44 . The output coil  45  in the external magnetic circuit  44  is used to quantify the amount of flux that the EMFV is able to control. 
     The present notional example shown in  FIG. 1  employs an embedded coil  16  to form the two flux control segments in the shunt core  14 . The coil  16 , when energized, produces a localized magnetic field around each void  12  and  15  in the shunt core  14 . The magnetic field causes the reluctance in the flux control segments  46  and  47  ( FIG. 4 ) to increase toward saturation. 
     The present notional example  FIG. 1  has the voids in the control segments  12  and  15  placed off center with respect to the shunt core  14  to allow the outer flux path  17  to saturate before the inner flux path  18  thus providing linear control of the permanent magnet  13  flux through the shunt  14 . 
     In one embodiment, M19 electrical steel laminations may be used for the shunt  14 . Note that  FIG. 2  shows the Stoletov curve  21  for the M19, which indicates that even when saturated the material is still quite permeable. Note that other types of material may be used in other embodiments. 
     In such an embodiment, the shunt core  14  may be fabricated with Carp 49 Permalloy. In  FIG. 3  the Stoletov curve  31  for the Carp 49 Permalloy  31  shows a reduction in coercion force that achieves saturation and also demonstrates the drop in permeability above saturation. 
     The magnetic flux control afforded by the present notional example  FIG. 1  can be quantified when placed in an external magnetic circuit  FIG. 4  and turned on and off. When the EMFV is deenergized the permanent magnet flux is constrained by the shunt core  14  as in  FIG. 5 . When the EMFV is energized the permanent magnet flux is free to energize the external magnetic circuit path as in  FIG. 6 . 
     In one embodiment, the amount of flux that the EMFV can control may be determined by the cross section of the permanent magnet and the width of the ferromagnetic shunt core shown in  FIG. 7 . In this embodiment, the magnet  73  and the shunt core  74  are made wider and then placed in the external magnetic circuit orthogonally as depicted in  FIG. 8  where the flux density in the external circuit would increase. 
     The present notional example  FIG. 1  is shown driven with a flux control coil  16 . The flux control coil  16  and the ferromagnetic shunt core  14  together form an electromagnet which when energized acts to reinforce a flux field produced by the permanent magnet  13 . When the flux control coil  16  is overdriven, beyond what is required to simply shift the permanent magnet flux into the external magnetic circuit as shown in  FIG. 8 , the extra flux produced by the “electromagnet” is passed into the external circuit to be added to the flux density quantified by the output coil  82 . 
     The EMFV is electrically driven to shift the permanent magnet flux out of the shunt core. The reactive power to overcome the inductance of the drive circuit is normally lost but in this case it may be recovered by the drive circuit to promote performance efficiency. 
     The conventional boost converter circuit takes power from the source and boosts the voltage to be delivered to the load. The Isolated boost converter in this notional example is different in that the power taken from the input source battery is able to be largely recovered and returned to the same source battery to be reused. This is accomplished, as seen in  FIG. 9 , by modifying the input of the conventional circuit design with the addition of an isolation power switch Q 1  and an integral bootstrap capacitor C 1  to establish the boost voltage threshold to force the recovered charge back into the source battery in support of the Recovery Cycle as shown in  FIG. 10 . 
     In  FIG. 9  the Drive Cycle is initiated by switches Q 1  and Q 2  turning on simultaneously and supplying drive current from the DC Link capacitor C 2  and the battery through D 3  to the EMFV which begins to shift the permanent magnet flux out of the shunt core. The boost capacitor C 1  is charged to the battery B 1  potential passively through R 1  in preparation for the Recovery Cycle. As the current flows through the EMFV the local flux builds until the control segments saturate at which point switches Q 1  and Q 2  open up and the magnetic flux which has built up collapses. 
     In  FIG. 10  the Recovery Cycle commences as the permanent magnet flux rushes back into the shunt core and induces a reverse polarity voltage into the EMFV control winding. The EMFV control winding voltage boosts the charge in the bootstrap capacitor C 1  and conducts through D 2  to charge the DC Link capacitor C 2  which in turn transfers charge back to the battery through the saturable reactor L 1 . When the Recovery Cycle concludes the Drive Cycle begins again. 
     The foregoing discussion discloses and describes exemplary methods and embodiments of the present disclosed disclosure. The disclosure is intended to be illustrative, but not limiting, of the scope of the apparatuses and methods, which are set forth in the following claims.