Electricity: motive power systems – Motor structure adjustment or control
Reexamination Certificate
2002-02-15
2004-03-30
Ro, Bentsu (Department: 2837)
Electricity: motive power systems
Motor structure adjustment or control
C310S114000, C310S268000
Reexamination Certificate
active
06713982
ABSTRACT:
The present invention relates to an electrical induction machine which uses a segmented coil construction to maximize active surface area of magnetic flux between rotor and stator elements, resulting in higher efficiency of flux utilization.
BACKGROUND OF THE INVENTION
Alternating current electric machines such as motors, transformers, and generators, are generally used because they are extremely rugged, reliable, easy to control, and in particular have a high torque capacity and high power density ratings. Induction machines operate on the principle that current traveling in stationary coils or windings of a stator produces a rotating magnetic field which in turn induces a current in a rotor occupying the space where the rotating magnetic field exists. The induced current in the rotor reacts with the rotating magnetic field to produce a rotational force.
Heretofore, it was believed that there was a fundamental limit to torque density in such machines. Although flux density is limited by material considerations, while current density is limited by (1) heating, (2) machine reactance, and (3) the fact that too much current density produces localized magnetic saturation, the present invention optimizes the configuration of the rotor and stator elements or primary and secondary elements so that the machine output can be increased without substantially increasing the volume of the machine. Conventional belief in the design of alternating current electric machines is that power density is limited and the only way to increase power output is to increase the volume of the machine.
The primary object of this invention is to provide an electrical machine having a high torque capacity for a given machine volume. A second object of this invention is to provide such an electrical machine in which the commonly accepted limit to torque density in electrical machines is overcome by utilizing the same magnetic flux among one or more parallel air gaps. A third object of this invention is to provide an electrical machine in which the magnetic flux is passed through multiple air gaps, inducing a surface current on the rotor at each air gap, thereby increasing the torque density for a give volume of the machine. A fourth object of this invention to provide such an electrical machine which may be operated as a rotary or synchronous machine. A fifth object of this invention to provide such an electrical machine in which force density is increased substantially by the number of air gaps present in the machine but the overall machine transverse dimension is increased only by a smaller factor because the magnetic return path remains nearly constant.
BRIEF SUMMARY OF THE INVENTION
The present invention is an alternating current (AC) electrical machine comprising:
(a) a stator having a plurality of stator elements in the form of annular disks, spaced apart from each other, each stator element comprising a plurality of magnetically isolated magnetic teeth;
(b) a rotor having a plurality of rotor elements mounted on a shaft, the rotor elements spaced from each other and interstitially disposed with the stator elements in an interdigitated manner;
(c) a plurality of electrical windings on each of the stator elements, each winding being associated with a group of magnetic teeth of the stator element, the windings being arranged such that, when energized with a current flowing in the windings, a magnetic flux is created in a first direction;
(d) means for completing a magnetic flux path in a second direction through corresponding groups of teeth on successive stator elements, and through the rotor elements.
The present invention may further comprise a modular control unit arranged to individually control electrical energy applied to each stator element, the control unit comprising:
(a) a microprocessor controller, a load sensing means and a plurality of stator control modules; each control module comprising an electrical switching device connected to a stator element; and wherein the microprocessor controller being responsive to the load sensing means to generate control signals to the control modules; and each control module being responsive to the control signals to control the flow of current to the connected stator element in a pulse-width control manner.
In the present invention each control module may further comprise current sensing means to sense current in the windings of the associated stator element and means to generate a corresponding signal to the microprocessor controller, the controller being responsive to the signal to compensate for the sensed current.
In the microprocessor controller of the present invention, the microprocessor controller may compare each current signal to a predetermined fault threshold to detect a winding fault and to cause that control module to deenergize the stator element in response to the detected fault, permitting the motor to continue to operate.
In the present invention, alternating current may be supplied from a multiphase source. The current sensing means is arranged to sense current in each individual phase, in each stator element winding. There is also a means to generate a corresponding sensing signal to the microprocessor controller. The controller is responsive to the sensing signal and generates control signals to the control modules to equalize the current in each phase of the stator windings. When current is supplied in this way, the microprocessor controller may compare each current sensing signal from each phase in the winding of each stator element to a predetermined fault threshold to detect a winding fault in a stator element, and cause the control module connected to that stator element to deenergize the stator element in response to the detected fault, permitting the motor to continue to operate.
In the present invention the load sensing means may comprise a motor speed sensor. The load sensing means may comprise a torque sensor.
In the present invention the rotor element may further comprise a plurality of radial grooves, the radial grooves causing air to move radially between adjacent rotor and stator elements to facilitate dissipation of heat generated within the rotor elements and the stator elements.
In the present invention, the housing may be constructed to facilitate airflow through the housing, or the housing may be of sealed, gas-tight construction.
Another embodiment of the present invention is a transformer comprising a primary, a secondary and a soft iron core,
the primary having a plurality of elements, each element being spaced apart from each other, and each element being in the form of an annular disk, each annular disk comprising a plurality of magnetically isolated magnetic teeth having wound thereon a plurality of electrical windings, the windings of each element of the primary being the same as any other element of the primary and;
the secondary having a plurality of elements, each element being spaced apart from each other, and each element being in the form of an annular disk, each annular disk comprising a plurality of magnetically isolated magnetic teeth having wound thereon a plurality of electrical windings, the windings of each element of the secondary being the same as any other element of the secondary; and
wherein the elements of the primary and the elements of the secondary are mounted on the soft iron core so that the elements of the secondary are spaced from each other and interstitially disposed with the elements of the primary in an interdigitated manner.
The transformer of the present invention may further comprise a modular control unit arranged to individually control electrical energy applied to each element of the primary and each element of the secondary, the control unit comprising:
a microprocessor controller, a load sensing means and a plurality of control modules;
each control module comprising an electrical switching device connected to either a primary or a secondary element;
the microprocessor controller being responsive to the load sensing means to generate control signals to the control modules;
E. I. du Pont de Nemours and Company
Ro Bentsu
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