1. Field of the Invention
The present invention relates to electrical machines, and more particularly to permanent magnet synchronous machines.
2. Description of Related Art
Synchronous machines can be used to rotate a prime mover to start the prime mover or be rotated by a prime mover to generate electricity. Some synchronous machines, such as permanent magnet (PM) synchronous machines, can be configured for both rotating the prime mover while in a start-up mode and be rotated by the prime mover in a generate mode. Such permanent magnet synchronous machines typically have permanent magnets disposed on a rotor portion of the machine and AC armature windings disposed on a stator portion of the machine. In start-up mode, current is supplied to the stator windings to generate a magnetic field. The generated magnetic field pushes against a magnetic field of the rotor permanent magnets, thereby applying a torque to the rotor and rotating the prime mover. In generator mode, the prime mover rotates the rotor and the rotor permanent magnets passed the stator windings, thereby inducing a current flow in the AC windings. In both modes there is a need to regulate the strength of the magnetic field created by the permanent magnets.
One way of regulating the magnetic field flux created by the permanent magnets of a PM synchronous machines is through the use of external solid-state converters. External solid-state state converters can provide flux control over a limited range. Another way of field flux regulation is by incorporating direct current windings on the surfaces of either the rotor permanent magnets or stator windings. Additional surface DC windings provide a greater range of control, albeit at the cost of increasing the diameter and size of the PM synchronous machine.
Such conventional methods and systems of regulating PM synchronous machine magnetic fields have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for a permanent magnet synchronous machine with improved magnetic flux excitation regulation. There is also a continuing need for smaller, more compact PM synchronous machines. And there remains a continuing need for PM synchronous machines that are easy to make and use. The present invention provides a solution for these problems.
The subject invention is directed to a new and useful electrical machine with a permanent magnet component radially spaced apart from an armature winding and a field excitation winding magnetically coupled with the permanent magnet component. The field excitation winding is configured and arranged to selectively intensify and de-intensify the magnetic field of the permanent magnet component for control of magnetic flux in the electrical machine.
In certain embodiments the permanent magnet component defines pole shoe slots housing the field excitation winding. The permanent magnet component may be a rotor and the winding armature may be a stator separated from the rotor by a radial gap. The permanent magnet component can further define pole shoe slots housing the field excitation winding. It is further contemplated that the slots housing the field excitation winding can be proximate the radial gap.
In accordance with certain embodiments the rotor can be a rotor core arranged radially inward of the stator. The rotor can also include embedded permanent magnets. In certain embodiments the stator may be a three-phase stator with slots housing respective AC windings.
The invention also provides an electrical machine with a permanent magnet component including a plurality of magnetic poles each with a respective embedded permanent magnet, and a plurality of field excitation windings with respective windings housed in a respective pole shoe slot of the permanent magnet component.
In certain embodiments the field excitation windings are connected together in series. It is also contemplated that, in certain embodiments, the field excitation windings are connected together in parallel. In accordance with certain other embodiments, the permanent magnet component is a rotor and the armature winding is a stator. The rotor and stator are separated by a radial gap and the pole shoe slots housing the field excitation windings are proximate the radial gap. It is also contemplated that the rotor is a rotor core arranged radially inward of the stator. It is further contemplated that the stator is a three-phase stator with slots housing respective AC windings.
These and other features of the systems and methods of the subject invention will become more readily apparent to those skilled in the art from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the devices and methods of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to certain figures, wherein:
Reference will now be made to the drawings wherein like reference numerals identify similar structural features or aspects of the subject invention. For purposes of explanation and illustration, and not limitation, a partial view of an exemplary embodiment of the permanent magnet synchronous machine in accordance with the invention is shown in
Referring now to
Rotor 10 has rotor core 12 and a plurality of permanent magnet components 14 arranged about its periphery. In the illustrated embodiment, rotor core 12 is disposed radially inward from permanent magnet components 14 and stator 20. Permanent magnet components 14 are coupled to rotor core 12 and define respective north/south poles on opposing ends as indicted in
With continued reference to
Referring to
Referring now to
Operatively, each permanent magnet component 14 generates a persistent magnetic field of constant magnetic flux at its respective pole. Field excitation windings 18 generate a magnetic field of variable magnetic flux. The variable magnetic field flux generated by windings 18 is determined by the amount of current flowing through the conductive paths 30 and 32 of field excitation windings 18. At each pole shoe, the persistent magnetic field flux of the permanent magnet and the variable magnetic field flux of the field windings cooperate to form an effective magnetic field flux. When voltage across terminals 36 and 38 is zero no current flows through field excitation winding 18, and the effective flux of permanent magnet component 14 corresponds to the constant field flux of the persistent magnetic field of permanent magnet component 14. When a positive voltage is applied at terminal 36 (as shown in
Referring now to
Excitation system 50 includes a rotating rectifier 60, a rotating exciter portion 70, a fixed exciter portion 80, and a DC controller 90. Rotating rectifier 60 and rotating exciter portion 70 are coupled with rotor 10 on shaft 32, and synchronously rotate together as an assembly. Fixed exciter portion 80 and a DC controller 90 are fixed with respect to shaft 32 and elements coupled thereto. DC controller 90 is electrically connected to fixed exciter portion 80, and is configured and adapted to generate an electromagnetic field about a coil of fixed exciter portion 80. Fixed exciter portion 80 is electromagnetically coupled rotating exciter portion 70 such that a set of wire coils successively pass into and out of the field generated by fixed exciter portion 80 as rotating exciter portion 70 rotates. The wire coils are electrically connected on an end to rotating rectifier 60, and collectively generate AC current which is supplied to rotating rectifier 60. Rotating rectifier 60 includes a diode bridge that, on one end receives an AC current from the rotating exciter portion 70, and on it other end it supplies DC current. Exciter 50 is a brushless exciter. As will be appreciated, embodiments of electrical machine 100 can include a solid state rectifier with slip rings and brushes.
Operatively, DC controller 90 is configured and arranged to supply and vary a DC current flowing through fixed exciter portion 80. Supplying DC current to fixed exciter portion 80 creates a magnetic field that induces alternating (AC) current in rotating exciter portion 70. Varying the supplied DC current changes the created magnetic field so as to vary the AC current in rotating exciter portion 70. The AC current induced in rotating exciter portion 70 is converted to DC current by rotating rectifier 60, such as by operation of a plurality of diodes for example. Rotating rectifier 60 supplies the DC current to the field excitation windings 18 disposed in pole shoe slots 16 of rotor 10. As would be appreciated, controlling the DC current supplied to fixed exciter portion influences the magnetic field modulation effected by the field excitation windings in rotor 10. Controlling can be done turning the DC current on and off, for example.
The DC voltage may be increased, decreased, or its polarity reversed, thereby inducing corresponding, e.g. offsetting or additive, variable magnetic flux from the field excitation windings. As would further be appreciated, DC controller 90 may further include a processor communicative with a non-transitory machine readable media with instructions recorded thereon that, when read by the processor, cause the DC controller to vary the DC current to control torque generated by the electrical machine 100 during start-up mode and/or voltage during generator mode.
With reference to
Operatively, when the field excitation windings are supplied with DC current, the rotor field winding flux can more readily reduce or magnify the magnetic flux of the permanent magnets depending on the direction of the current applied to the field excitation windings. This allows for regulating magnetic flux within the machine by either weakening or strengthening the magnetic field, controlling output voltage when the machine is in generator mode and controlling torque when the machine is control in start-up mode. Embodiments of electrical machine 100 provide better effect of flux weakening and magnification, and therefore provide voltage or toque control. Embodiments of electrical machine 100 are also relatively compact because the field excitation windings are positioned within the rotor permanent magnets, and not on either of the inner stator surface or rotor outer surface. For this same reason, embodiments of electrical machine 100 also require less copper in the rotor field winding, and have relatively high power density. They can also be easier to manufacture and provide more space for permanent magnets.
The methods and systems, as described above and shown in the drawings, provide an electrical machine with superior properties including control of the magnet flux between the electrical machine rotor permanent magnets and winding armatures. While the apparatus and methods of the subject invention have been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the spirit and scope of the subject invention.