US 6,177,746 B1 · Low inductance electrical machine

Abstract

A low inductance electrical machine that may be used as an alternator or motor with low armature inductance is disclosed. Arrangements of complementary armature windings are presented in which the fluxes induced by currents in the armature windings effectively cancel leading to low magnetic energy storage within the machine. This leads to low net flux levels, low core losses, low inductance and reduced tendency toward magnetic saturation. The inclusion of additional gaps in the magnetic circuit allows for independent adjustment of air gap geometry and armature inductance. Separately excited field arrangements are disclosed that allow rotor motion to effect brush-less alternator or brush-less motor operation. An exemplary geometry includes a stator including two annular rings and a concentric field coil together with a rotor structure separated from the stator by four air gaps.

A low inductance electric machine comprising:

a. a stator structure including:
i. an armature structure made substantially of low loss magnetic material;
ii. one or more phases of armature windings coupled to said armature structure, wherein each of said phases of armature windings includes a series circuit of one or more complementary pairs of armature windings arranged so that magnetic flux, within said armature structure, induced by a current through said complementary pairs of armature windings tends to cancel and thereby results in low inductance in each of said phases of armature windings independent of current in other of said phases of armature windings;
iii. an inner annular ring of low loss magnetic material located coaxially within said armature structure;
and
iv. an annular field coil of insulated turns of copper, fixed coaxially between said inner annual ring and said armature structure to provide means for an externally applied electric current to excite and control a magnetic field within said stator structure;
b. a rotor structure including two rotor disks, each of said disks arranged to hold a set of equal numbers of radial rotor pole bars associated with said stator structure;
wherein each of said sets of rotor pole bars are shifted circumferentially with respect to one another by one pole spacing;
wherein there is one of said complementary pairs of armature windings for each of said phases of armature windings for each of said pairs of rotor pole bars;
wherein said rotor structure is separated from said stator structure by multiple air gaps;
and wherein said rotor structure is configured to create magnetic poles which interact with magnetic flux induced by electrical currents in said armature windings and said field coil to provide means for electromechanical energy conversion;
c. a plurality of magnetic pathways established to conduct flux induced by electrical current in said field coil, each of said magnetic pathways passing through a pair of said rotor pole bars, said pair including one member from each of said sets or rotor pole bars, and each of said magnetic pathways including four air gaps in series, with magnetic flux flowing serially through the following magnetic circuit:
i. axially and circumferentially through said armature structure;
ii. then through a first one of said air gaps, said first air gap established between said armature structure and a first member of said pair of rotor bars, said first member located on first of said rotor disks;
iii. then substantially radially through said first rotor bar,
iv. then axially through a second one of said air gaps, said second air gap established between said first rotor bar and said inner annular ring;
v. then axially through said inner annular ring;
vi. then through a third one of said air gaps, said third air gap established between said armature structure and a second member of said pair of said rotor bars, said second member located on second of said rotor disks;
vii. then substantially radially through said second rotor bar;
and
viii. finally through a fourth one of said air gaps, said fourth air gap established between said armature structure and said second rotor bar to complete said magnetic circuit;
wherein said second and third of said air gaps, which are associated with said inner annular ring, provide means to:
ix. control the reluctance of said magnetic circuit substantially independently of the air gap length of said first and fourth air gaps, which are associated with said armature structure, in order to reduce the inductance of said armature circuits caused by flux induced in said magnetic circuit;
x. allow relative motion between said rotor structure and said inner annular ring;
and
xi. force flux flow to spread evenly across said second and third air gaps and thus across the face of said inner annular ring, thereby reducing flux concentrations and tendencies toward local magnetic saturation effects;
d. a shaft placed coaxially within said armature structure and said inner annular ring, said shaft preferably being of non-magnetic material in order to effectively remove it from said magnetic circuit;
e. means to couple said electrical machine to an external source of mechanical rotary power, or an external mechanical load, and means to hold said stator structure and said rotor structure so that one is stationary while the other rotates.

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Low inductance electrical machine

Life of this patent

Low inductance electrical machine

Life of this patent

Abstract

Claims20