Saturable reactor and converter for use thereof

• US 5,764,494 A
• Filed: 03/13/1997
• Issued: 06/09/1998
• Est. Priority Date: 03/13/1997
• Status: Expired due to Term

• Current Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Original Assignee: Lockheed Martin Corporation (Martin Marietta Corporation)
• Inventors: Schutten, Michael Joseph, Earls, William George
• Primary Examiner(s): BERHANE, ADOLF D
• Application Number:
  US08/800,721
• Time in Patent Office: 453 Days
• Field of Search: 363/15, 363/17, 363/20, 363/22, 363/56, 363/95, 363/98, 363/132, 336/83, 336/84 R, 336/155, 336/218
• US Class Current: 363/17
• CPC Class Codes: H02M 3/28 using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac

Abstract

A switching converter achieves improved regulation range by the use of a saturable reactor in series with a transformer primary. The saturable reactor uses a conventional magnetic pot core including a magnetic shell and center post. The location at which the post joins the shell is perforated to reduce the cross-section of magnetic material, so that, at low reactor currents, incremental inductance is established by the gap between post and lid, and at high reactor currents, the incremented inductance is established by saturation at the base of the post. Perforation at the base of the post also results in generation of heat at a location immediately adjacent the flat bottom of the pot core.

Claims

1. A saturable reactor arrangement, comprising:

a ferromagnetic pot core arrangement having, when assembled, the general exterior form of a right circular cylinder, said right circular cylinder defining first and second flat, mutually parallel, approximately circular ends, an axis, and a fastener clearance aperture passing through said right circular cylinder and said first and second ends centered on said axis, said pot core arrangement being divided into two portions along a division plane perpendicular to said axis and lying between said first and second ends, at least one of said portions of said pot core arrangement including a ferromagnetic shell portion which, together with the other of said portions of said pot core arrangement, defines said right circular cylindrical exterior form, said ferromagnetic shell portion of at least one of said portions of said pot core arrangement having a thickness selected to define a cavity within said shell, said cavity being in the general shape of a right circular cylinder defining a bottom adjacent one of said first and second ends, said cavity of said one of said portions of said pot core arrangement having an axial post defining proximal and distal ends, said proximal end of said post of said one of said portions of said pot core arrangement being monolithically affixed to said bottom, said post extending distally from said bottom, parallel with said axis, toward said division plane, said post containing said fastener clearance aperture;

said post of said one of said portions of said pot core arrangement further including

(a) a distal portion of said post in the form of an annular ring of ferromagnetic material lying in a plane parallel to said division plane;

(b) a plurality of apertures extending through the side of a second portion of said post and said bottom, which second portion of said post lies between said distal portion of said post and said bottom, said plurality of apertures being located so as to divide said second portion of said post into a plurality of legs extending from said bottom to said distal portion of said post, for supporting said distal portion of said post at a predetermined location relative to said division plane,

(c) each of said legs of said plurality of legs being monolithically affixed to said bottom along a support surface having a first dimension equal to the thickness of said bottom, and a second dimension equal to the width of that one of said legs being supported,

(d) the surfaces of said support areas of said plurality of legs having a cumulative area less than that of said post and less than that of said shell, so that magnetic fields generated within said cavity of said pot core, and flowing through said post and said shell, must pass through said cumulative area of said support areas, and so that magnetic saturation of said pot core occurs preferentially at said surfaces of said support areas, whereby the heat generated by magnetic saturation of said core preferentially occurs adjacent one of said first and second ends of said pot core arrangement.

2. A saturable reactor arrangement according to claim 1, further comprising a thermally conductive, nonmagnetic material filling said plurality of apertures extending through the side of said second portion of said post and said bottom, to aid in transferring heat away from said support surfaces.

3. A saturable reactor arrangement according to claim 2, wherein said thermally conductive material is thermally conductive epoxy.

4. A saturable reactor arrangement according to claim 2, further comprising a thermally conductive heat sink affixed to that one of said first and second ends of said adjacent said thermally conductive, nonmagnetic material, for aiding in transferring heat away from said support surfaces.

5. A saturable reactor arrangement according to claim 1, wherein said legs support said distal portion of said post at a predetermined location relative to said division plane which leaves a gap between said distal portion of said post said other one of said portions of said pot core arrangement, whereby the magnetic reluctance of said pot core arrangement is established by said gap in a linear operating regime, and by said support areas in a saturated operating regime.

6. A saturable reactor arrangement according to claim 1, further comprising a conductive coil wound about said post of said one of said portions of said pot core assembly;

and further comprising;

a transformer including a primary winding and a secondary winding, said primary winding being serially connected with said coil to define a series circuit;

a controllable switched bridge circuit coupled to said series circuit, and adapted for applying alternating voltage thereto, as a result of which electrical drive is generated at said secondary winding of said transformer;

a unidirectional conducting device arrangement coupled to said secondary winding of said transformer, for rectifying said electrical drive;

a substantially linear reactor coupled to said unidirectional conducting device arrangement and to a load, for supplying electrical drive current to said load; and

control means coupled to said controllable switched bridge circuit, for causing the switches of said bridge circuit to switch in a manner tending to maintain constant electrical drive to said load.

7. A dc-to-dc converter for driving a load, said dc-to-dc converter comprising:

a switched bridge circuit including load terminals;

a series circuit coupled to said load circuit of said bridge circuit, said series circuit including a saturable reactor and the primary winding of a transformer, said transformer also including secondary windings at which electrical drive is generated in response to operation of said bridge circuit;

an arrangement of unidirectional current conducting devices coupled to said secondary windings, for rectifying said electrical drive;

a linear reactor coupled to said arrangement of unidirectional current conducting devices and to said load, for tending to maintain a characteristic of the electrical drive to said load;

said saturable reactor comprising;

(a) a ferromagnetic pot core arrangement having, when assembled, the general exterior form of a right circular cylinder, said right circular cylinder defining first and second flat, mutually parallel, approximately circular ends, an axis, and a fastener clearance aperture passing through said right circular cylinder and said first and second ends centered on said axis, said pot core arrangement being divided into two portions along a division plane perpendicular to said axis and lying between said first and second ends, at least one of said portions of said pot core arrangement including a ferromagnetic shell portion which, together with said other of said portions of said pot core arrangement, defines said right circular cylindrical exterior form, said ferromagnetic shell portion of said one of said portions of said pot core arrangement having a thickness selected to define a cavity within said shell, said cavity being in the general shape of a right circular cylinder defining a bottom adjacent one of said first and second ends, said cavity of said one of said portions of said pot core arrangement having an axial post defining proximal and distal ends, said proximal end of said post of said one of said portions of said pot core arrangement being monolithically affixed to said bottom, said post extending distally from said bottom, parallel with said axis, toward said division plane, said post containing said fastener clearance aperture;

(b) said post of said one of said portions of said pot core arrangement further including

(i) a distal portion of said post in the form of an annular ring of ferromagnetic material lying in a plane parallel to said division plane;

(ii) a plurality of apertures extending through the side of a second portion of said post and said bottom, which second portion of said post lies between said distal portion of said post and said bottom, said plurality of apertures being located so as to divide said second portion of said post into a plurality of legs extending from said bottom to said distal portion of said post, for supporting said distal portion of said post at a predetermined location relative to said division plane,

(iii) each of said legs of said plurality of legs being monolithically affixed to said bottom along a support surface having a first dimension equal to the thickness of said bottom, and a second dimension equal to the width of that one of said legs being supported,

(iv) the surfaces of said support areas of said plurality of legs having a cumulative area less than that of said post and less than that of said shell, so that magnetic fields generated within said cavity of said pot core, and flowing through said post and said shell, must pass through said cumulative area of said support areas, and so that magnetic saturation of said pot core occurs preferentially at said surfaces of said support areas, whereby the heat generated by magnetic saturation of said core preferentially occurs adjacent one of said first and second ends of said pot core arrangement.

8. A saturable reactor arrangement according to claim 7, further comprising a thermally conductive, nonmagnetic material filling said plurality of apertures extending through the side of said second portion of said post and said bottom, to aid in transferring heat away from said support surfaces.

9. A saturable reactor arrangement according to claim 8, wherein said thermally conductive material is thermally conductive epoxy.

10. A saturable reactor arrangement according to claim 8, further comprising a thermally conductive heat sink affixed to that one of said first and second ends of said adjacent said thermally conductive, nonmagnetic material, for aiding in transferring heat away from said support surfaces.

11. A saturable reactor arrangement according to claim 7, wherein said legs support said distal portion of said post at a predetermined location relative to said division plane which leaves a gap between said distal portion of said post and the other one of said portions of said pot core arrangement, whereby the magnetic reluctance of said pot core arrangement is established by said gap in a linear operating regime of said saturable reactor, and by said support areas in a saturated operating regime.