WO1988007782A1

WO1988007782A1 - Electric generator

Info

Publication number: WO1988007782A1
Application number: PCT/AU1988/000080
Authority: WO
Inventors: John Van Der Wolf; Ronald Van Der Wolf
Original assignee: Wolf John V D; Wolf Ronald V D
Priority date: 1987-03-24
Filing date: 1988-03-22
Publication date: 1988-10-06
Also published as: AU616885B2; AU1540288A

Abstract

A wind-powered magneto-electric generator of which magnetic rotors (36, 37) are on a common shaft (17) direct-driven from a wind-turbine (Figs, 8, 9 and 10) to generate in stators (18, 19) an electromotive force (EMF) which is controlled relative to the input power by switching the stators into series or parallel in response to the shaft speed and a signal derived and fed back from the EMF function.

Description

ELECTRIC GENERATOR

This invention relates to electric generators including alternators, dynamos, magnetos, and so-called *»* alternating current (AC) and direct current (DC)

5 generators, and including generators powered by wind and/or water power or suchlike bountiful but uncon¬ trollable and relatively unpredictable source of input energy.

A typical generator as known and used 10 hitherto has included a collector such as an armature consisting essentially of an arrangement of coiled wires or other suitable conductor, magnetic field means for generating or^'establishing a magnetic field in the vicinity of the armature, and means for moving the 15 field means relatively to the armature to induce in the^• latter a voltage or electromotive force (EMF) which, according to long-established principles, depends on the nature of the armature, the strength of the field, and the rate at which their relative movement causes 20 lines of magnetic force to cut the conductor.

Usually either the armature or the field means are held stationary and the other is rotated on a shaft powered from a suitable source.

The field means may itself comprise a system 25 of conductive windings (field windings) excited by electric current to generate the required magnetic field. In the compound-wound type, the field system includes series and shunt windings in series and parallel respectively with the armature. The respec- 30 tive inductances or number of turns of these windings are such as to flatten the output voltage/load current _a curve. Sometimes the series windings have fewer turns or a smaller inductance or collective capacity than the shunt windings. It is also known to regulate the 35 output voltage by means of a rheostat in a shunt field circuit.

The generators to which this invention relates also include the so-called magneto-electric machines wherein the field means consist of one or more permanent magnets e.g. a combination of horseshoe magnets constituting a stator, or a bar or other suitable magnet fixed to the input shaft providing rotating field means within a stationary system of collector windings. At this stage it appears that significant advantages of the invention may be obtain¬ able with generators which do not require commutators e.g. magneto-electric generators of the latter type wherein an alternating or otherwise varying voltage or current is obtained using a rotating permanent magnet. However the invention may also have reference to generators of the kind having brushes with slip-rings or split-rings, such as for collecting voltage or current from a moving armature, or supplying excitation current to rotating electromagnetic field means. Excitation current can be provided by any suitable EMF source such as a battery, or an accum¬ ulator charged from the generator output.

The mechanical energy input may be a shaft rotated by a wind- steam- or hydro-turbine, or, as in motor car or other engines _t from the crankshaft of an internal-combustion engine with which the generator is associated in an electrical system including a battery, an induction coil, and means for distributing high voltage to spark plugs of the engine in a suitably timed sequence.

A typical electrical generator system includes a battery or accumulator, and means for modifying or regulating the output voltage so that the battery receives and accumulates electrical charge from the generator. Cut-outs may be provided in order to interrupt the circuit when (1) the battery has received a maximum safe charge, and (2) to prevent discharge of the battery through the generator when the output * voltage falls to an unacceptably low level vis-a-vis

5 that of the battery.

It has often been found that electric generators vary widely in efficiency depending upon the input revolutions per minute. Sometimes there is no effective or efficient generation of useful output 10 until the available RPM or mechanical energy input reaches a substantial value.

A further shortcoming of some prior generat¬ ors is that they draw current even when there is no output EMF. 15 An object of the invention is to provide a generator which adapts itself to vagaries of power input so as to put out a useful and reasonably predict¬ able EMF.

Another object is match input energy require^- 20 ments of a generator with the required output EMF and thereby improve the overall efficiency and usefulness of the machine.

These and other objects and advantages will become apparent hereinafter. 25 According to the present invention in one form, an electrical generator having an input rotary shaft adapted to be turned by torque applied by dynamic pressure of wind and/or water, electromagnetic field means on said shaft, and a stator co-operable with said _s 30 field means, is characterized in that said stator comprises a system having a plurality of stator _β elements with means responsive to the rotational speed of the shaft and/or to the generator output, to change the manner of connection or interconnection of said 35 stator elements and/or to disconnect one or some of said elements from the system so as to vary the effective collection capability of the stator according to the available input power and the required output power or EMF. But in order that the invention may be better understood reference will now be made to the accompany¬ ing drawings which are to be considered as part of the specification and read herewith. In the drawings:

Fig. 1 shows, in transverse and axial cross- sections respectively, a stator/rotor disposition in a practical embodiment of^* the invention with the stator (shaded) outside the rotor;

Fig. 2 is similar to Fig. 1 but with the stator inside the rotor; Fig. 3 is a schematic circuit diagram of a practical embodiment of electrical generator wherein the field means are rotating "permanent" magnets, there being two rotor/stator assemblies;

Fig. 4 is similar to Fig. 3, but with four rotor/stator assemblies;

Fig. 5 is similar to Figs. 3 and 4 using one rotor, and a stator with two sets of windings;

Fig. 6 is similar to Fig. 5 but wherein the field means are an electro-magnet; Fig. 7 is a schematic diagram of a practical embodiment of circuit from converting an output AC or DC voltage to a desired AC or DC voltage function;

Fig. 8 is a perspective view showing a four- vaned Savonius wind turbine for driving a generator according to the invention;

Fig. 9 is a top-plan view of the wind turbine shown in Fig. 8, and

Fig. 10 is a diagrammatic cross-section of the wind turbine shown in Figs. 8 and 9 showing the arrangement of vanes in relation to each other and to the axis of rotation.

Referring to the drawings in more detail, Figs. 1 and 2 show how a stator 11, 12 and rotor 13, 14 respectively can be relatively located in two practical embodiments of the invention.

Fig. 3 is a circuit diagram of a magneto- electric generator wherein rotors 15, 16 of a permanent-magnet type fixed to wind-turbine shaft 17 are respectively associated with stators 18, 19 in which lastmentioned is induced an EMF (usually variable AC or DC) which is conveyed via switching means (to be described more fully hereinafter) to output terminals 20 and 21,^' having been regulated as desired by voltage regulator 22. Tachometer 23 senses the rotational speed, acceleration or some other parameter of motion of shaft.17, and sends a signal to limiter 24 accord¬ ingly.

The rotor may, for example, be an eighteen- pole rotor. Advantageously the magnets are of a ceramic type.

Stators 18 and 19 have respective sets of terminals (25, 26) and (27, 28) and an associated switch 29 has switch^' elements 30 and 31 operable together or separately by relays or any other suitable devices in response to signals from 24. In the drawing, 30 and 31 are shown in their respective first , positions, whereby the windings of rotors 18 and 19 are connected in series. If, now, both 30 and 31 are switched over i.e. to their second positions, 18 and 19 are connected in parallel.

If 30 and 31 are in the second and first positions respectively, stator 19 becomes ineffective because although 26 and 28 are connected (via link 32) , terminal 27 is removed from the circuit. It follows that when switch elements 30 and 31 are in their second and first positions respectively, the stator assembly is comprised entirely of the windings of 18.

Conversely when 30 and 31 are in their first and second positions respectively, 25 and 27 become connected via link 33, and 26 is removed from the cir¬ cuit, and the stator assembly of the generator is comprised entirely of 19.

Therefore depending upon the level or availability of power put in by shaft 17, the effective collection capability of the collector means represent¬ ed by 18 and 19 can be varied by using different positions of the switches in response to the generated or prevailing EMF and/or a parameter of the shaft rotation. Lines 34 and 35 feed output voltage and current signals respectively from voltage regulator 22 to limiter 24.

If, in use under sustained high wind condit¬ ions only one of the generators represented by 15, 18 and 16, 19 has been operating or if the two have been operating in parallel for example, and the wind speed drops, the combined effect of signals from tachometer 23 and from output voltage and current through lines 34 and 35 respectively, may cause 30 and 31 to take up their first positions, as shown in Fig. 3, and the stators will operate together and in series and the output voltage will be represented by the sum of the voltages induced in each.

Figure 4 is a variant of Fig. 3 with four, instead of two, generator components. These consist of rotors 36 to 39 on a common shaft 17 and stators 40 to 43 respectively. The stators have respective sets of terminals (44, 45) (46, 47) (48, 49) and (50,-51), and can be connected, disconnected or interconnected by three switches 52, 53 and 54 each having a pair of switch elements (55, 56), (57, 58) and (59, 60) operable together or separately between first and second positions as described in Fig. 3. They are shown in their first positions, whereby the stators are all connected in series.

Each switch is essentially a five-terminal device, comprising a first terminal which is contacted by both of the relevant switch elements when the switch is in the first position, second and third terminals from adjacent stators and which are connected to the first terminal when the switch is in the first posi¬ tion, and fourth and fifth terminals to which the switch elements connect the second and third terminals, respectively, when the switch is in the second posi- tion.

Thus for switch 53, for example, the first to the fourth terminals are 62, 47, 48, 66 and 67 respect¬ ively. The third and fourth terminals of all switches are connected by lines 70 and 71 respectively to the extreme terminals 51 and 44 of the stator system.

If switch 53 is switched to its second position, the other two switches remaining in their first position, the stators are connected in a series/parallel arrangement i.e. the series combination of 40 and 41 is connected in parallel with the series combination of 42 and 43.

Clearly any number N of stators or sets of windings can be used, with N-l switches for intercon¬ necting them as exemplified above by reference to Fig. 3 (N=2) and Fig. 4 (N=4) . Various combinations of settings of the switches and switch elements gives various series/parallel combinations of stators or sets of windings, and/or removal of up to N-l of the windings from the stator system. For example, in Fig. 4 if 48 only is switched over, then 41, 42 and 43 are isolated from the system, and 40 are the only effective windings. In general, the greater the diversity of the inductances of the respective rotors, the greater will be the diversity of generative effect obtainable from the total of 2 ^~ switch settings. If desired, all inductances may be different.

Fig. 5 shows a generator with one permanent- magnet type rotor 72 and a twin-wound four- erminal stator 73 and switch means 74 similar to those prev- iously described. Fig. 6 shows a similar generator, but having electro-magnetic field means excited via lines 75, 76 from limiter 24. If desired, provision may be made for the excitation current to be switched off when the shaft speed falls below a prescribed minimum. This -can be achieved by a suitable signal from 22, 23 and 24.

An accumulator or other storage_^ device can be included at any suitable part of the circuit e.g. across terminals -20, 21. Thus the generator can be or operate as a storage of electrical power.

Fig. 7 shows one way of changing modifying or refining the outside signal appearing at terminals 20, 21 e.g. to a standard 240 volt/50 cycle AC voltage or EMF. Due to vagaries of the input supply, the output EMF function at 20, 21 will usually vary considerably. If it be "alternating" in any sense, its frequency will often depend closely upon the speed of the wind or water - if such a power source is used. - At all events it may be desired to modify the signal to a constant- level DC or a signal closely approximating a sine-wave of substantially constant frequency and amplitude, so as for example to be a safe and useful energy source for standard household appliances.

Thus the signal across 20, 21 may be a varying DC of mean level e, .g. 340 volts. Converter, oscillator and regulator circuits 77, 78 and 79 respectively operate on the signal to produce across 80, 81 a suitably regulated and stable-frequency signal (e.g. 240 volt/50 cycle) for the required purposes. The motive means may be a wind turbine, preferably of a type which turns even at low wind- speeds, although its rotational speed may approach an upper limit which will not be exceeded even in the highest winds experienced in the region. These characteristics may.assist in enabling the generator to be direct-driven i.e. without a gearbox.

Figures 8 to 10, illustrate a Savonius wind turbine of a kind found eminently suitable for ^"driving a generator 82 according to the invention. Savonius, Dariaz and suchlike turbines may be preferred if they commence rotating in low winds and if their speed asymptotes to a maximum as the wind-speed increases.

The turbine shown in Figs. 8 and 9 comprises four sets of vanes fixed to vertical shaft 17. In Fig. 10, wind coming from the direction shown by the arrow in Fig. 10 is caught by the inside of bucket 83 and is deflected back through gap 84 into bucket 85, producing a counter-clockwise torque exceeding the clockwise torque of the wind pressure on the outside of bucket 85.

Dynamic water pressure e.g. in a river or tideway, may be similarly employed.

Dariaz and suchlike turbines may require a starting torque or impulse. Such may be provided by a small subsidiary Savonius turbine or windmill.

Although the invention has been particularly described by reference to a wind-generator, its principles are applicable to a wide variety of natural or artificial power sources, however predictable or unpredictable, controllable or uncontrollable. It may be used in conjunction e.g. with a tide-power device or in electrical systems associated with petrol or diesel internal combustion engines and for a wide variety of other purposes.

Especially, the invention makes possible the efficient generation of useful EMF when the shaft speed is very low by conventional standards. By means of the invention, useful outlets have be^'en obtained down to 5 revolutions per minute.

Claims

The claims defining the invention are as follows:

1. An electric generator having collector and field means, and motive means for moving them relative¬ ly so as to induce an electromotive force in the former, characterized by means responsive to said force and/or to a parameter of the motion, for varying the effective collection capability of said collector means.

2. An electrical generator having an input rotary shaft adapted to be turned by torque applied by dynamic pressure of wind and/or water, electromagnetic field means on said shaft, and a stator co-operable with said field means, characterized in that said stator comprises a system having a plurality of stator elements with means responsive to the rotational speed of the shaft and/or to the generator output, to change. the manner of connection or interconnection of said stator elements and/or to disconnect one or some of said elements from the system, so as to vary the effective collection capability of the stator according to the available input power and the required output power or EMF.

3. An electric generator including an input shaft, motive means for driving said shaft, magnetic field means on said shaft, and a stator co-operable with said field means, characterized in that said stator comprises a plurality of diversely interconnect- ible sets of windings of differing inductances, and switching means responsive to input and/or output parameters of the generator for automatically connect¬ ing, interconnecting or disconnecting the windings and thereby altering their net generative effect to maintain a desired output level.

4. A generator as claimed in claim 3 wherein there are N said sets of windings, and wherein said switching means comprises N-l switches which when all in a first position connect all N windings in series, when all in a second position connect all N windings in parallel and which in other settings provide for various series/parallel combinations of said sets of windings, and/or for removal of up to N-l of said windings from the stator system.

5. A generator as claimed in claim 4 wherein each switch has two elements operable together or separately.

6. An electric generator including an input shaft, vane means on said shaft rendering the shaft rotatable by wind pressure, a rotor comprising electro¬ magnetic field means on said shaft, a stator co- operable with said field means, current supply means for the field means, and.first and second output terminal links connected respectively to first and second terminals of the stator, characterized in^" that the stator includes a first set of windings between said first terminal and a third terminal and a second set of windings between the second and a fourth terminal of the stator, and further characterized by relay switch means which in a first position connect the third and fourth terminals to provide a series combination of said windings and in a second position disconnect the third from the fourth terminals and connect the first to the fourth and second to the third terminals to provide a parallel combination of said windings, tachometer means for sensing the rotational speed of the shaft, and means for moving the switch means in response to signals derived from the tacho¬ meter means and/or a generated EMF function.

7. An electric generator as claimed in claim 6 including limiter means associated with the second output terminal for controlling the field current and for preventing current supply to the field means whenever the shaft speed falls below a prescribed minimum.

8. A generator as claimed in any one of the preceding claims motivated by a Savonius or Dariaz wind-turbine direct coupled to said shaft.

9. A method of generating a substantially predictable EMF from a substantially unpredictable mechanical input, characterized by the step of varying the inductance of collector means according to the EMF and/or a parameter of relative motion between magnetic or electromagnetic field means and said collector means.

10. An electrical generator substantially as herein described with reference to the accompanying drawings.