AU2013100035A4 - Permanent Magnet Alternator for Low Speed Applications - Google Patents

Abstract

An alternator consisting of two or more rotor discs in which a plurality of rare earth magnets are config ured as a polar array around a central shaft with their polarity alternately arranged parallel to the shaft. At least one disc stator secured radially to the frame, consisting of coils wound around inductive ferrite cores, configured in a similar polar array and suspended between the two rotor discs. When the rotor assembly is turned, the stator coils are so arranged as to coaxially align with the rotor magnets, thus interacting with the magnetic flux and generating electrical AC output power. Figure 1

Description

- 1 Permanent Magnet Alternator for Low Speed Applications BACKGROUND [001] There is a commercial need in the free energy field for a suitable high flux density slow revving electrical generator as a suitable interface for small to medium wind, wave and water turbine systems. The difficulty with most commercially available alternators and generators is that they are designed for use with high revving internal combustion engines and are therefore unsuitable for the task. [002] The design of most modern electrical alternator/generators in which the stator normally encases the rotor radially (with the salient poles perpendicular to the shaft)is also unsuitable as the laminated protrusions of the stator can accommodate only a few turns of wire thus limiting the generation of flux in the wire at slow revs. The insertion of the wire into the slots is also cumbersome compared to winding wire on a bobbin. In addition, the magnetic flux can only penetrate the coils from one side thus limiting the transfer of energy to only shallow penetration of the coils despite the practice of closing the magnetic circuit of the stator. All in all the modern permanent magnet alternator/ generator is unnecessarily complex and inefficient at low speeds. SUMMARY OF THE INVENTION [003] In Faraday terms it matters not if many turns of wire are cut slowly or a few turns of wire are cut quickly just as long as the same magnetic flux cuts the same number of turns in unit time. Both will produce the same outcome. Therefore for a slow revving alternator/generator it is necessary to either maximize the number of wire turns or the intensity of the flux or both to generate the maximum electrical output in the shortest possible time. This can easily be achieved if the coils are fixed in a circle on a disc with their cores oriented parallel to the axis of the circle to form a stator and abutted by two outer discs each containing a similar polar array of rare earth magnets and mounted on a shaft symmetrically with the stator. The number of coils used and the number of turns used on each core is no longer limited as in the conventional arrangement, because the magnetic flux can now penetrate through the entire coil. Efficiency is therefore maximized. The use of inductive ferrite cores will also improve hysteresis efficiency and simplify assembly compared with conventional soft iron laminations. [004] Unfortunately, if the number of coils in the polar array and the number of magnets in each disc are the same then the system will tend to lock up magnetically. To overcome this problem it is necessary to vary the number of coils and magnets in the polar array so as to neutralize this binding effect on start up. Ideally the ratio of magnets to coils should be 4 to 3 so that all forces are equally balanced when at rest. When the discs are started they will tend to follow the desired path or rotation due to compatible magnetic attraction and repulsion of the interacting flux fields. Cogging is virtually eliminated. Once the system starts to rotate then the output will increase exponentially in proportion to radial speed of the rotors with each variation in design conforming to its own individual parabolic curve.

-2-~ [005] If the coil core diameter and magnet pole diameter are the same and the gapping between any two adjacent coils are arranged to be the same as the cores then flux losses and overheating can be reduced to a minimum. This is a simple design problem when bobbin wound coils are used in a disc design, but can be a complex and expensive exercise when using a conventional radial layout. The air gap between the face of the coil cores and the magnets also needs to be adjusted for maximum efficiency which again is a simple spacing exercise when parallel coincident discs are used but is a difficult problem in radial designs because the gap cannot be easily adjusted without re-machining. [006] The use of neodymium rare earth magnets in the rotors gains a considerable advantage over other permanent magnet materials; the neodymiums have a higher flux density and a very slow flux erosion curve. Although it is common practice to close the magnetic circuit with a keeper, my experiments have shown that it matters not in this design if the magnetic circuit is closed or open, the output is the same. However, the use of a keeper ring attached to the outer rotor discs (not shown in the drawings) to close the circuit may prevent external interference and other magnetic problems. [007] There is of course no need for slip rings or any external power source as is the case with electromagnets. However, as the flux cannot be varied when using permanent magnets an external power regulator is required. Should it be desired to control the output by varying the magnetic flux then suitable excited-field electromagnets may be used in place of the neodymiums. BRIEF DESCRIPTION OF DRAWINGS [008] Figure 1 is an isometric view of the invention showing the stator and rotor assemblies combined. [009] Figure 2 is a cut-away center section of the view shown in Figure 1. [010] Figure 3 is an isometric view of the stator assemblies containing the inductive coil assemblies. [011] Figure 4 is an isometric view of one of the two identical permanent magnet rotor assemblies. [012] Figure 5 shows a plan view of one of the coil and core assemblies with the bobbin side removed. (013] Figure 6 is a side elevated center section of Figure 5 showing the coil winding, bobbin and ferrite core. [014] Figure 7 is a characteristic layout of coil assemblies and permanent magnets showing the preferred spaced relationship between the magnets and ferrite cores of the coils. [015] Figure 8 is a center section view cut alone the shaft showing another embodiment of the invention in which multiple disc sets are mounted symmetrically along one shaft. [016] Figure 9 is yet another embodiment of the invention in which coils and magnets are arranged on common discs in multiple sets.

~ 3~ DESCRIPTION OF PREFERRED EMBODYMENT [017] Referring now to the figures, a stator (1) and a pair of rotors (2A) and (2B) are shown in operative spaced relationship in Figure 1 and Figure 2. For the sake of simplicity the casing is not illustrated, and it will be understood that the rotor assemblies (2A) and (2B) are normally mounted on a shaft for rotation in suitable bearings located in the casing. As apparent from Figure 4, the rotors (2A) & (2B) comprise two identical discs around which are mounted a plurality of permanent magnets (4A) & (4B) fixed to the discs (2A) & (2B) by clamping screws {not shown} in a ridged structure. The rotor discs (2A) and (2B) are preferably constructed of non magnetic material such as plastic or aluminium with each disc secured to the shaft by a suitable boss and the magnetic polarity of the magnets (4A) & (4B) aligned to each other and parallel to the shaft as shown in Figure 2. Soft iron keeper ring discs {not shown} may also be fitted to the outer face of each end rotor, radially aligned, and in contact with the permanent magnets to complete the external magnetic circuit of the assemblies. The permanent magnets (4A) & (4B) are arranged in an equally spaced circular polar array around the shaft with the polarity of each adjacent magnet pole in the circle configured alternately north and south so when the discs (2A) & (2B) are rotated an alternating field is generated at any fixed point between the intervening gap of the discs (2A) & (2B). [018] Interposed between the rotor discs (2A) and (2B) as depicted in Figure 1 & 2 is a stationary stator disc (1) secured radially to the outer casing {not shown} and designed in like manner to the rotor discs with a plurality of bobbin style coil assemblies (5) (Fig.5 & 6) arranged in an evenly spaced circular polar array, each wired to the other in delta, star of compound configuration as is well known in the art and according to the dictates of the connected load and application of the system. Figure 3 shows the design of the stator (1) and the layout of the coil assemblies (5). Figure 3 also shows the ferrite cores (3) of the coil assemblies (5) protruding through and secured to two outer retainer discs (7A) and (7B), the poles of each ferrite core (3) being finished flush with the outer face of the retaining discs (7A) and (7B). The design of each coil assembly (5) is shown in more detail in Figure 5 and Figure 6 in which the coil (6), bobbin (8) and ferrite core (3) are clearly shown in plan Figure 5 and side elevation center section Figure 6. [019] When the stator (1) is assembled together with the rotor discs (2A) and (2B) in an operative spaced relationship as in Figure 1 and 2, the mean radius of the polar coordinate array of all three discs (1), (2A) and (2B) are identical such that a coincident alignment is momentarily achieved between each paired set of magnets (4A) & (4B) and the coil assemblies cores (3) in the stator (1) as the rotors (2A) & (2B) are caused to revolve through the axis of rotation. An alternating electrical current is therefore inductively generated in the coils as the coil assemblies cut through the alternating magnetic flux field of the revolving rotor assemblies. [020] Figure 7 is a graphical presentation of the preferred radially spaced relationship of the magnets (4A) (& identically 4B not shown) overlaying the coil cores (3). As can be seen from this embodiment of the invention there are twelve coil assemblies (5) divided into four sets of three coils assemblies each, with the output connected to a three phase external rectifier {not shown). The magnetic array on disc (2A) contains sixteen magnets (4A), which is configured into four sets of four magnets each as shown in Figure 4. One matching set of three coils assemblies (5) and four magnets (4A) is indicated by the arrows in Figure 7. As disc (2A) and (2B) are identical the same arrangement also applies to disc (2B). The preferred embodiment of this invention should therefore comply with these relationships. [021] It is clear to those experienced in the art that in the related position of the coils and magnets shown in Figure 7, that the rotors (2A) & (2B) to which the magnets (4A) & (4B) are fixed has no propensity to revolve in either direction being equally attracted and repelled in all directions. However, should the said rotors be prompted to move in either direction then the resulting attraction and repulsion between the magnets and the ferrite cores will tend to perpetuate the rotation in the same direction. It is by this means that cogging and magnetic lockup are virtually eliminated. This phenomenon, however, also depends on the spacing and angle between components. If the angle and spacing are too wide, then cogging will occur. If the angle and spacing are too narrow, then the system will tend to lock up. There is therefore an optimum setting at which stating resistance is negligible. [022] Figure 8 is another embodiment of the invention which features multiple disc sets on a common shaft. [023] Figure 9 is yet another embodiment of the invention in which many additional coil-magnet sets have been fitted to one common disc set.

Claims (1)

1. A permanent magnet alternator/generator for low speed applications comprising: two or more disc shaped rotors and one or more disc shaped stators; said rotors being fitted parallel to each other in a spaced relationship and mounted in a balanced radially spaced relationship to each other on a rotational drive shaft, with said rotors supporting a plurality of permanent magnets arranged radially around the fulcrum of said rotors in an evenly spaced relationship to each other, with the axis of polarity of each permanent magnet arranged parallel to the axis of the said rotational shaft, and with the polarity of each said magnet in the array configured in reverse polarity to its adjacent neighbor in the same circular array, and each adjacent parallel pair or said rotor discs being so arranged on the said shaft as to form a fixed alignment of the said magnets in the circular array of each said rotor disc such that the polarity between each pair of aligned magnets is also compatibly aligned magnetically, and on the outer face of the two outer said rotor discs may be attached a flat radial ring of soft iron of like mean diameter to the magnetic array of the said magnets in such a manner as to close the magnetic field of the said alternator/generator, with each said disc shaped stator fixed by its circumference to the inner casing of said alternator/generator in a spaced relationship to the said rotor discs and coaxially arranged with said stators in an evenly spaced relationship between each pair of said rotors, and with each said stator fitted with a circular radial array of round bobbin shaped coils with the axis of each coil also parallel to the axis of said rotational shaft, and the circular array of said coils arranged to coincide with the circular array of the said magnets fitted to the said rotors so that the axis of each coil and the axis of each permanent magnet pair may align in an operationally spaced relationship of the alternator/generator assemblies in which each said round bobbin shaped coil is wound on a circular former which in turn is mounted coaxially and evenly spaced on an inductive circular ferrite core exhibiting an hysteresis characteristic curve suitable to the speed of rotation of the said alternator, and to assist in easy starting of the said alternator/generator, a set of three said coil assemblies on each stator are matched to a set of four said permanent magnets on each said rotor disc which may be configured with an acceptable number of complete related sets in each radial array, provided the array of said coils on the stators and said magnets on the rotors are evenly spaced and the mean diameter of the circular array on all said rotor discs and said stator discs are the same: Operationally the said rotor assemblies revolve within the said casing generating a series of alternating magnetic fields between any two said rotor discs and the said fixed interposing stator coils which in turn generates an alternating electrical current in the said coils in accordance with the discoveries of Michael Faraday (17891-1867) and Nicola Tesla (1856-1943); the electrical output of the said coils may then be wired in any acceptable form to suit operational and load requirements. ...000... Barry Hilton Inventor