AU616885B2 - Electric generator - Google Patents

Description

4

J

A 04 WORLD INEL~ULPR P TY OROANIZATION International Bureau 0

PCT

INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 4 (11) International Publication Number: WO 88/ 07782 H02K 21/12, 21/26, 23/50

A

H02K 23/36, H02P 9/02, 9/14 Al(43) International Publication Date: 6 October 1988 (06.10.88) H02P 9/48 (21) International Application Number: PCT/AU88/00080 4 (22) International Filing Dgte: (31) Priority Application Number- (32) Priority Date: (33) Priority Country: 22 March 1988 (22.03.88) PI11049 24 March 1987 (24.03,87) Published61 85 With in ati al a~ hr t. 8 I D DEC 1988

AUSTRALIAN

2 NOV 1988 PATENT OFFICE Applicants and Inventors: VAN DER WOLF, John VAN DER WOLF, Ronald [AU/AU]; 67 Forest Park Road, Upwey, VIC 3158 (AU), (74)Agent: NICHOLLS, Peter, Norman; 48-50 Bridge Road, Richmond, VIC 3121I (AU), (81) Designated States-, AT (European patent), AU, BE (European patent), CH (European patent), DE (European patent), FR (European, patent), GB, GB (European patent), IT (European patent), LU (European patent), NL (European patent), SE (European patent), US, (54) Title. ELECTRIC GENERATOR (57) Abstract A wind-powered magneto-electric generator of Which magnetic rotors (36, 37) are on a common shaft (17) direct-drlyven from a wind-turbine (Figs, 8, 9 and 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, 12 torque which is a function of the power being zenerated. WO 88/07782 PCT/A U88/00080 ELECTRIC

GENERATOR

This invention relates to electric generatLors including alternators, dynamos, imagnetos, and so-called alternating current (AC) and dirie2ct current (DC) generators, and including generators powered by wind and/or water power or suchlike bountiful but uncontrollable and relatively unpredictable source of input energy.

A typical generator as known and used 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 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 thefi relativ- movement causes lines of magnetic force to cut the c nductor.

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

The field means may itself comprise a system 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 respective inductances or number of turns of these windings are such as to flatten the output vol~tage/load current curve. Sometim~es the series windings. have fewer turns or a smaller inductance or collective capacity than the shunt windings. it is also known to regulate the output voltage by means of a rheostat in a shunt field LY4 WO 88/07782 PCT/A U88/00080 2 circuit.

The generators to which this invention 1 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 Smagnets 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 obtainable 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 accumulator 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, 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 inclvuos a battery or accumulator, and means for modifying or regulating the output voltage so that the i battery receives and accumulats electrical charge from the generator. Cut-outs may be provided in order to I_ i I- 1 ,WO 88/07782 PCT/AU88/00080 3 interrupt the circuit when the battery has received a maximum safe charge, and to prevent discharge of the battery through the generator when the output voltage falls to an unacceptably low level vis-a-vis 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 until the available RPM or mechanical energy input reaches a substantial value.

A further shortcoming of some prior generators is that they draw current even when there is no output EMF.

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 predictable EMF, Another object is match input energy requirements 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.

L t-Aelden-te- the--rzr form, an electrical generator having an input ary shaft adapted to be turned by torque appl by dynamic pressure of wind and/or water, elect agnetic field means on said shaft, and a stat co-operable with said field means, is characteri in that said stator comprises a system h ng a plurality of stator elements with m s responsive to the rotational speed of the sha and/or to the generator output, to change the m er of connection or interconnection of said sAQ5-4{k /i 'a hi ii i 3a According to the present invention an electric generator includes a rotary shaft adapted to be driven by an unpredictably variable power source, magnetic rotor field means on the shaft, a stator system co-operable with said field means and having a plurality of stator elements, means for switching said elements into or out of the system and for altering the series/parallel relationship of the "in" elements to provide a number of stator modes of different generative capabilities, and a limiter co-operable with said switching means to reduce the generative capability as the power drops while there is a lull in said power source, thereby reducing the resisting torque experienced by the shaft the while, enabling the rotor field means in effect to "freewheel" pro tern, and to increase said generative capability as the available power increases.

The invention also provides a method of generating an electric current in a circuit including a stator system by causing an associated magnetic rotor field means to be turned by torque due to wind or some other unpredictably variable power source, against a resisting torque which is a function of the power being generated, characterized by automatically reducing the generative capability of the stator system as a function of said power so as to reduce said resisting torque during a power lull thereby enabling the rotor field means in effect to "freewheel" pro tern.

M41 i WO 88/07782 PCT/AU88/00080 4effective collection capabilit -or according to the avail ower and the required output zpower or EMr. But in order that the invention may be better understood reference will now be made to the accompanying drawings which are to be considered as part of the specification and read herewith. In the drawings: Fig. 1 shows, in transverse and axial crosssections 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 fourvaned 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, 1Q 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 PCT/AU881 00 08 0 WO 88/07782 a.0 WO 88/07782 PCT/A 88/00080 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 magnetoelectric 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 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 pends a signal to limiter 24 accordingly.

The rotor may, for example, be an eighteenpole 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. Cn 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 WO 88/07782 PCT/AU88/00080' -6and 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 front the circuit, 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 represented 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.

I:f, in use under St.stainied high wind conditio; s only one of the generatoz- represented by 15, 18 and 16, 19 has been operating or if the two have b en operating in parallel for example, and th~e 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 su~m of the voltages induced in each, Figure 4 is a variant of Fig. 3 with four, instead olt two, generator components. These consist of rotors o.05 to 39 on a commron 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 WO 8/0782 1/10P CT/A U88/00080 <3i"ii"r L-i WO 88/07782 PCT/AUL88/00080 7 switch elements (55, 56), (57, 58) and 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 position, and fourth and fifth terminals to which the switch elements connect the second and third terminals, respectively, when the switch is in the second position.

Thus for switch 53, for example, the first to the fourth terminals are 62, 47, 48, 66 and 67 respectively. 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-1 switches for interconnecting tuem as exemplified above by reference to Fig.

3 and Fig, 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-1 of the windings from the stator system, For example, in Fig. 4 if 48 only is switched over, then 41, 42 and 43

K

WO 88,107782 PCT/AU88/00080' 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 gonerative effect obtainable from the total of 2 2N-2 switch settings. If desired, all inductances may be different.

Fig. 5 shows a generator with one permanentmagnet type rotor 72 and a twin-wound four-terminal stator 73 and switch'means 74 similar to those preyiously 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 21 e.g, to a standard 240 volt/50 cycle AC voltage or EMF. Due to vagaries cf 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 constantlevel 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 340 volts, Converter, p1 s 'I 'WO 88/07782 PCT/A U88/00080 oscillator and regulator circuits 77, 78 and 79 respectively operate on the signal to produce across 81 a suitably regulated and stable-frequency signal 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 windspeeds, 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.7 eaur oeU r &t~on oi cr.c&cn i~n spee 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.

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 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 O" f 'iA

Y

oF: A*a 1//10 ',VVO 88/07782 PCAU8800()8(r WO 88/07782 PCT/AU88/00080 10 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 been obtained down to revolutions per minute.

I

Claims (3)

1. An electric generator including a rotary shaft adapted to be driven by an unpredictably variable power source, magnetic rotor field means on the shaft, a stator system co-operable with said field means and having a plurality of stator means for switching said elements into or out of the system and for altering the series/parallel relationship of the "in" elements to provide a number of stator modes of different generative capabilities, and a limiter co-operable with said switching means to reduce the generative capability as the power drops while there is a lull in said power source, thereby reducing the resisting torque i" experienced by the shaft the while, enabling the rotor field means in effect to "freewheel" pro tern, and to increase said generative capability as the available power Increases.

2. A generator as dlatmed in claim 1 wherein said limiter is responsive to S* 3 tachometer means responsive to the rotational speed of said shaft.

15. 3. A generator as claimed in claim 2 wherein said rotor field means is electromagnetic and the limiter controls field current supplied to said field means, and cuts off said field current whenever the shaft speed falls below a prescribed minimum. 4. An electrical generator substantially as herein described with reference to the accompanying drawings. A method of generating an electric current in a circuit including a stator system by causing associated magnetic rotor field means to be turned by a torque due to wind or some other unpredictably variable power source, against a resisting 12 torque which is a function of the power being generated, characterized by automatically reducing the generative capability of the stator system as a function of said power so as to reduce said resisting torque during a power lull thereby enabling the rotor field means in effect to "freewheel" pro tern. DATED this t94day of 1991. JOH VANj DER WOLF and RONALD VAN DER WOLF By their Patent Attorney: PETER Ij-LS