The invention relates generally to electrical machines and, more particularly, to a dual magnetic phase stator lamination for use in permanent magnet electric machines having the magnets in the stator.
The usage of electrical machines in various industries has continued to become more prevalent in numerous industrial, commercial, and transportation industries over time. In an attempt to realize high performance in electric machines, the choice of using permanent magnet (PM) materials is getting more and more popular for many applications. In such machines, the PMs can either replace electromagnets in traditional designs, or novel topologies can be developed to make the best use of the properties and characteristics of PMs.
One PM electrical machine topology that has been developed is referred to as “stator permanent magnet machines,” which are electrical machines that are designed such that the PMs in the machine are positioned on the stator. Stator permanent magnet machines can thus refer to, but are not limited to, permanent magnet flux switching machines, permanent magnet flux reversal machines, and doubly-salient permanent magnet machines.
Stator permanent magnet machines are typically designed such that the PMs in the machine are embedded in the stator. To embed the PMs, a plurality of discrete stator laminations comprised of a soft, magnetic material are manufactured so as to have open slots formed therein, with the open slots being formed to accommodate placement of the permanent magnets therein. In each of the stator laminations, “bridges” are included on one or both sides of the permanent magnets to provide mechanical strength to the lamination. Typically, these bridges are formed of the same soft, magnetic material as the rest of the lamination, so as to enable formation of the lamination via a single cutting operation and from a single piece of magnetic material, rather than a segmented or multi-part lamination.
While the bridges found in typical stator laminations of a stator permanent magnet machine provide the mechanical robustness necessary for the laminations to be easily formed (such as in a single cutting operation), the bridges also can have a negative impact on the machine's power capability. That is, as the bridges are formed of the same soft, magnetic material as the rest of the stator lamination, the bridges form a leakage path for the permanent magnet flux, thereby reducing the machine's power capability. Furthermore, as the magnetic bridges of the stator laminations need to be thick in order to provide sufficient mechanical strength to the lamination, this thickness of the bridges provides a larger leakage path for the permanent magnet flux, so as to further reduce the machine's power capability.
Therefore, it would be desirable to provide stator laminations for a stator permanent magnet machine that can be formed via a single cutting operation, while minimizing the permanent magnet flux leakage typically associated with laminations formed from a single material so as to increase the machine's power capability.
The invention is directed to stator laminations for a stator permanent magnet machine. The stator laminations are formed of a dual magnetic phase material and are heat treated such that portions of each stator lamination are rendered non-magnetic, so as to block paths of permanent magnet flux leakage in the stator lamination.
In accordance with one aspect of the invention, a permanent magnet electrical machine includes a rotor mounted for rotation about a central axis and a stator positioned about the rotor and comprising a plurality of stator laminations, wherein each of the stator laminations is composed of a dual magnetic phase material and includes a first stator lamination portion comprising a magnetic material and a second stator lamination portion comprising a non-magnetic material, the second stator lamination portion comprising an area positioned adjacent to each of a plurality of permanent magnets embedded in the stator lamination. The second stator lamination portion comprises a heat treated portion of the stator lamination, with the heat treating of the second stator lamination portion rendering the dual magnetic phase material of the stator lamination non-magnetic at the locations of the second stator lamination portion.
In accordance with another aspect of the invention, a method for manufacturing a permanent magnet electrical machine includes the steps of providing a rotor mounted for rotation about a central axis and forming each of a plurality of stator laminations for use in forming a stator, wherein forming each of the plurality of stator laminations further includes the step of providing a non-segmented stator lamination formed of a dual magnetic phase material that is magnetic in a first state and non-magnetic in a second state, with the non-segmented stator lamination being provided in the magnetic first state. Forming each of the plurality of stator laminations further includes the steps of embedding a plurality of permanent magnets in the stator lamination and heat treating the stator lamination at a plurality of pre-determined locations adjacent to the plurality of permanent magnets so as to cause the pre-determined locations of the stator lamination to transition to the non-magnetic second state. The method further includes the step of joining the stator laminations to form a stator, with the stator being positioned about the rotor so as to enable rotation of the rotor within the stator.
In accordance with yet another aspect of the invention, a stator lamination for a permanent magnet electrical machine includes an outer casing, a plurality of teeth extending radially inward from the outer casing, and a plurality of openings formed in one of the outer casing and the plurality of teeth, wherein a bridge structure is formed adjacent each opening to provide mechanical stability to the stator lamination. The stator lamination also includes a plurality of permanent magnets embedded in the stator lamination within the plurality of openings, such that the plurality of permanent magnets in one of the outer casing or the plurality of teeth. The stator lamination is formed of a dual magnetic phase material, with the bridge structures being heat treated so as to be in a non-magnetic state and a remainder of the stator lamination being in a magnetic state, such that the bridge structures block a leakage path of permanent magnet flux.
Various other features and advantages will be made apparent from the following detailed description and the drawings.
The drawings illustrate preferred embodiments presently contemplated for carrying out the invention.
In the drawings:
Referring to
The stator section may include an outer casing 108 (sometimes referred to as the “back iron” or “yoke”), and one or more teeth 110 each extending, say, radially inward from the outer casing. Conductive windings 112 can be wound around respective teeth 110. Insulation 114 can be included so as to provide electrical isolation between the outer casing 108/teeth 110 and the conductive windings 112. The stator 102 also includes one or more permanent magnets 116 that are embedded in the stator (i.e., either in the teeth 110 or in the casing 108), with the magnets being magnetized such that the magnetization polarities of the magnets alternate circumferentially around the stator 102.
During operation of the stator permanent magnet machine 100, the shaft 118 and rotor 104 rotate about the axis a. Depending on whether the stator permanent magnet machine 100 is a generator or a motor, electric current in the conductive windings 112, interacting with magnetic fields associated with the magnets 116, will either be induced by or cause rotation of the rotor 104. In the former case, work done on the shaft 118 can induce rotation of the shaft and rotor 104 and current flow in the windings 112, while in the latter, current injected into the windings can cause rotation of the rotor and shaft as the rotor attempts to bring the rotor teeth 120 positioned thereon to a position of minimum reluctance with respect to the stator teeth 110.
Regarding the stator 102 shown in
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Another permanent magnet flux-switching machine stator lamination 162 is shown in
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Another stator lamination 202 for use in a doubly salient permanent magnet or hybrid excited machine is shown in
Beneficially, embodiments of the invention thus provide a stator permanent magnet machine having stator laminations formed of a dual magnetic phase material. The dual magnetic phase material of the stator laminations can be heat treated to make portions of the stator lamination non-magnetic. Specifically, bridges on the stator lamination positioned adjacent the permanent magnets, on either one side or both sides of each permanent magnet, can be made non-magnetic. By making the bridges non-magnetic, any leakage path through the bridges for the permanent magnet flux is blocked, so as to increase the power capability of the machine.
In using dual magnetic phase material for the stator lamination, the non-magnetic bridges can be made thick as needed for robustness. Additionally, when using dual magnetic phase material for the stator lamination, the lamination can be cut as one whole lamination (i.e., integral) without segmentation such that the lamination has a uniform coefficient of thermal expansion, thereby easing a shrink fitting of a motor casing or a cooling jacket about the stator and reducing the cost of the stator assembly for certain type of stator PM machines, like flux switching machines, since there is no need to assemble several separate lamination segments. While such integral/singularly formed laminations have been previously available, they have not included non-magnetic portions that function to block a leakage path of the permanent magnet—thereby limiting the power capability of prior art machines.
Therefore, according to one embodiment of the invention, a permanent magnet electrical machine includes a rotor mounted for rotation about a central axis and a stator positioned about the rotor and comprising a plurality of stator laminations, wherein each of the stator laminations is composed of a dual magnetic phase material and includes a first stator lamination portion comprising a magnetic material and a second stator lamination portion comprising a non-magnetic material, the second stator lamination portion comprising an area positioned adjacent to each of a plurality of permanent magnets embedded in the stator lamination. The second stator lamination portion comprises a heat treated portion of the stator lamination, with the heat treating of the second stator lamination portion rendering the dual magnetic phase material of the stator lamination non-magnetic at the locations of the second stator lamination portion.
According to another embodiment of the invention, a method for manufacturing a permanent magnet electrical machine includes the steps of providing a rotor mounted for rotation about a central axis and forming each of a plurality of stator laminations for use in forming a stator, wherein forming each of the plurality of stator laminations further includes the step of providing a non-segmented stator lamination formed of a dual magnetic phase material that is magnetic in a first state and non-magnetic in a second state, with the non-segmented stator lamination being provided in the magnetic first state. Forming each of the plurality of stator laminations further includes the steps of embedding a plurality of permanent magnets in the stator lamination and heat treating the stator lamination at a plurality of pre-determined locations adjacent to the plurality of permanent magnets so as to cause the pre-determined locations of the stator lamination to transition to the non-magnetic second state. The method further includes the step of joining the stator laminations to form a stator, with the stator being positioned about the rotor so as to enable rotation of the rotor within the stator.
According to yet another embodiment of the invention, a stator lamination for a permanent magnet electrical machine includes an outer casing, a plurality of teeth extending radially inward from the outer casing, and a plurality of openings formed in one of the outer casing and the plurality of teeth, wherein a bridge structure is formed adjacent each opening to provide mechanical stability to the stator lamination. The stator lamination also includes a plurality of permanent magnets embedded in the stator lamination within the plurality of openings, such that the plurality of permanent magnets in one of the outer casing or the plurality of teeth. The stator lamination is formed of a dual magnetic phase material, with the bridge structures being heat treated so as to be in a non-magnetic state and a remainder of the stator lamination being in a magnetic state, such that the bridge structures block a leakage path of permanent magnet flux.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
This invention was made with Government support under contract number DE-EE0005573 awarded by the United States Department of Energy. The Government has certain rights in the invention.