Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-06-01
2003-06-03
Ramirez, Nestor (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S268000, C310S181000, C310S186000, C310S179000, C310S156070
Reexamination Certificate
active
06573634
ABSTRACT:
TECHNICAL FIELD
The field of the invention is brushless machines, including both AC and DC machines, including both motors and generators, and including induction machines, permanent magnet (PM) machines and switched reluctance machines.
DESCRIPTION OF THE BACKGROUND ART
There are three major types of brushless electric machines available for the electric vehicle (HV) and hybrid electric vehicle (HEV) drive systems. These are the induction machine, the PM machine, and the switched-reluctance machine.
In an induction motor, operation at higher speeds is provided by field weakening in the constant power speed range. An induction machine is robust and requires only a relatively simple power electronics drive. However, the rotor of an induction machine produces considerable resistance heating as a result of current produced in the rotor during operation. In an electrical vehicle this would provide a significant source of heat that should be cooled.
Permanent magnet (PM) machines have been recognized for having a high power density characteristic. A PM rotor does not generate copper losses. One drawback of the PM motor for the above-mentioned applications is that the air gap flux produced by the PM rotor is fixed, and therefore, a sophisticated approach is required for high speed, field weakening operation. Another constraint is that inductance is low, which means that current ripple must be controlled.
The switched reluctance motor is another type of machine that does not have the copper loss of the induction machine. However, a complicated control and sensor system is required to provide sufficient torque over its range of operation.
The direct current (DC) brush-type motors have a long history. The maintenance of the brushes that conduct the electric current from the stator to the rotor is a major reason limiting the application development. Hsu, U.S. Pat. No. 5,929,579, issued Jul. 27, 1999, discloses advanced brush and soft commutation technologies.
Electric and magnetic phenomena are closely related in such machines. As disclosed in Hsu, U.S. patent application No. 09/475,591, filed Dec. 3, 1999, and entitled “Hybrid Secondary Uncluttered Machine,” DC magnetomotive force (mmf) may be transferred from a stator to a rotor without using brushes and without a significant core loss. As further disclosed in Hsu, U.S. Pat. No. 6,057,622, issued May 2, 2000, and entitled “Direct Control of Air Gap Flux”, a stator core section with a winding can be added to the basic stator to reduce flux in the main air gap for field weakening operation. When the magnetic flux is guided by ferrous material, flux leakage can become a major problem. PM elements may be used to “guide” the flux as disclosed in Hsu, “Flux Guides for Permanent Magnet Machines,” PES/IEEE Transactions on Energy Conversions Paper No. PE-007EC, March, 2001. In order to differentiate the flux leakage between the rotor poles and the flux leakages elsewhere in an electric machine, the flux leakage between rotor poles is referred to herein as “flux diffusion.”
In order to overcome the above problems, including “flux diffusion,” the invention provides a novel machine described below.
SUMMARY OF THE INVENTION
This invention provides a new type of machine for transferring mmf from a stationary winding to a rotor without the use of brushes or rotating windings.
The invention is incorporated in a brushless electric machine having a stator and a rotor spaced from the stator to define a main air gap. The rotor has an axis of rotation and has pairs of rotor pole portions disposed at least partly around the axis of rotation and facing the main air gap, with the pairs of rotor pole portions being spaced from each other to provide spaces. A stationary excitation winding with at least one coil is adapted for receiving direct current from an external source and is positioned next to the rotor so as to induce a rotor-side flux in the rotor which increases a resultant flux in the main air gap when the direct current is of a first polarity and which reduces resultant flux in the main air gap when the direct current is of a second polarity opposite said first polarity. PM material is disposed in spaces between the rotor pole portions to inhibit the rotor-side flux from leaking from said pole portions prior to reaching the main air gap.
The invention provides stationary windings in the stator and avoids the use of any rotating windings. This allows for cooling systems to be added to cool the areas around the stationary windings.
The invention is applicable to both AC and DC machines, and to both motors and generators.
The invention is disclosed in terms of a preferred embodiment in an axial gap configuration, however, the invention is also applicable to radial gap machines.
The invention is also practiced in a method of controlling flux in a brushless electrical machine having a stator with a stationary, primary excitation winding and a rotor separated by a main air gap, with the rotor having a portion facing the main air gap. The method comprises inducing a first flux in the rotor from the stator across the main air gap; passing a direct current through a stationary coil; positioning said stationary coil so as to induce a second flux in the rotor from a position separated from the main air gap by at least a portion of the rotor; and providing portions of PM material at least partly around said portions of the rotor separating the coil from the main air gap so as to prevent leakage of the second flux induced in the rotor before reaching the main air gap.
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.
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Aguirrechea J.
Quarles & Brady LLP
Ramirez Nestor
UT-Battelle LLC
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