WO2009004633A2

WO2009004633A2 - Variable speed generator with voltage regulation system based on the stator and/or rotor winding length

Info

Publication number: WO2009004633A2
Application number: PCT/IL2008/000922
Authority: WO
Inventors: Dror Nadam; Rahamim Ben-David
Original assignee: Dror Nadam; Rahamim Ben-David
Priority date: 2007-07-05
Filing date: 2008-07-06
Publication date: 2009-01-08
Also published as: WO2009004633A3

Abstract

A system and device for providing constant voltage power, or optionally (and alternatively) voltage determined according to a set point or a set point range, by a generator, through control of the length of the stator and/or of the rotor winding of the generator. The length of the stator and/or rotor winding is controlled according to the rotational speed of the shaft of the generator, such that variations of the rotational speed of the shaft are compensated by changes to the length of the winding, preferably by adjusting a relative location of the stator winding which is relative to the location of the rotor winding.

Description

VARIABLE SPEED GENERATOR WITH VOLTAGE REGULATION SYSTEM BASED ON THE STATOR AND/OR ROTOR WINDING LENGTH

FIELD OF THE PRESENT INVENTION The present invention is related to a system and device for generating electricity according to a constant output yet with potentially variable speed, and in particular, to such a system and device which feature a voltage regulation system.

BACKGROUND OF THE PRESENT INVENTION The generation of electricity through the use of electrical generators is important for modern life. These generators require some source of external energy to operate, which may for example be some type of fossil fuel and/or renewable energy. The generator then consumes the energy source in order to generate electricity. However, it is important that the power output remain constant in order for the generated electricity to be usable.

The power output can remain constant if the shaft speed of the generator remains constant. However, the shaft speed of the generator cannot always be held to a constant rate. Therefore, some generators have relied on maintaining at least a minimum speed, such that the power output provided is determined according to the minimum speed of the shaft. If the shaft speed increases beyond the minimum, the excess power produced is discarded and hence is wasted.

Various solutions have been attempted but none has completely solved the problem for alternating current (AC) generators. For example, US Patent Application No. 2004/0257050 describes a method and device for constant current generation, which attempts to overcome drawbacks associated with potentially variable shaft speed through controlling the current that is output by the generator, thereby achieving a constant level of output current. Therefore, the described invention relates to current stabilization which differs in nature from the suggested voltage regulation. Various attempted solutions for achieving stabilized voltage output have included using inertia or friction as a mean of moderating the shaft speed fluctuations; using torque control in order to control the shaft speed; or converting the fluctuating

AC electricity to DC electricity, and then converting it again into the standard grid AC power. Clearly all of these methods are very wasteful of energy.

In an effort to use sources of renewable energy, systems and devices have been introduced which use "natural" energy such as wind, through the use of wind turbines; sun, through the use of solar panels; water power, such as wave or tidal power; and the like. Wind energy may be particularly variable, given that wind tends to increase and decrease in power, and/or change direction, quite regularly. However, all of the "natural" energy sources may be expected to suffer from instability of power levels. Thus, for renewable energy, the ability to convert non-stable mechanical power to stable electrical power has major demand in a variety of applications.

Various solutions have been proposed in this area to overcome the instability of renewable energy sources, particularly with regard to wind generation. For example, US Patent No. 7068015 provides a solution for wind power by adjusting the magnetic field according to the rotation speed of the wind turbine. These adjustments are made according to feedback determined by measuring voltage of the output signal or current. The actual control of the magnetic field is provided by "injecting" high voltage to the generator's stator, which requires an AC/DC high voltage rectifier. It is clearly disadvantageous to require such a rectifier.

US Patent Application No. 2004/0119292 provides a method for controlling the shaft speed of the generator by controlling its torque, a solution which is disadvantageous as noted above. The taught method further requires a diode rectifier for operation, which is another disadvantage.

US Patent No. 5083039 controls the power output by controlling the magnetic field of the generator, by controlling the stator current. However, changes to the stator current cause changes to the generator torque. In order to compensate for changes to the torque, the shaft speed is controlled by changing the pitch of the "wings" or blades of the turbine, which may be disadvantageous due to wind conditions, and which is disadvantageous in any case because it requires an additional expenditure of energy. US Patent No. 6137187 is similarly disadvantageous as it requires a pitch control system.

SUMMARY OF THE INVENTION

The background art does not teach or suggest a system or device for maintaining constant electrical output for an AC (alternating current) generator that is efficient even if the rotational speed of the shaft is variable. The background art also does not teach or suggest such a system or device which is suitable for energy sources that are, by their nature, highly variable. The background art also does not teach or suggest such a system or device which is suitable for "natural" energy sources, particularly wind.

The present invention overcomes these drawbacks of the background art by providing a system and device for generating a constant voltage level with an AC or DC generator even if the rotational speed of the shaft fluctuates, by controlling the length of the winding interacting with the magnetic field, such that optionally and preferably the length of the stator winding of the generator is controlled by being altered; alternatively or additionally the length of the rotor winding may optionally be altered.

The electro magnetic force induced by an AC or DC generator is governed by Faraday's law:

EMF=ώ x L x B x sin(θ) In which:

EMF (electromagnetic field) is the voltage of the output signal, ώ is the tangential speed of the winding. L is the length of the winding that crosses the magnetic flux. B is the magnetic field intensity. sin(θ) is the sin of the angle between the winding & the magnetic flux.

The above equation indicates that the peak voltage of the output signal of the generator is dependent on the shaft rotation speed, which in turn depends upon the mechanical power used to rotate the shaft. If the level of mechanical power is variable then the shaft rotation speed is in turn variable. However, even if the shaft rotation speed is variable, one method to provide a constant voltage output is to control the length of the winding subjected to the magnetic field influence, thus changing the effective length of the stator and/or rotor winding and thereby maintaining the peak voltage at a substantially constant level. Therefore, the present invention does not require the shaft rotation speed to be constant, which is useful for a wide variety of applications, including but not limited to power generation by renewable energy or "natural" energy sources or any other energy source having variable output. Instead, according to preferred embodiments of the present invention, the measurement of the shaft speed is used to control the length of the stator and/or rotor winding (L) through a feedback or control mechanism according to the speed of rotation of the shaft, thereby providing a constant voltage output and hence stable power generation. Preferably, the effective stator and/or rotor winding length is adjusted, by which is meant that the length of at least a portion of the stator winding which crosses the magnetic flux is adjusted. The actual physical length of the stator and/or rotor winding optionally and preferably remains unchanged.

According to preferred embodiments of the present invention, control of the effective length of the stator and/or rotor winding of the generator is preferably provided through changing the location of the stator winding relative to the rotor winding. The relative location of the stator and/or rotor winding is preferably determined by an adjustment motor. The rotation speed of the shaft of the generator is measured; according to this measurement, the operation of the adjustment motor is then used to increase or decrease the effective stator and/or rotor winding length, thereby maintaining a constant voltage output even if the rotation speed of the shaft varies. The winding length may optionally be changed by altering the effective stator and rotor overlap, and/or optionally and alternatively (or additionally) by altering the effective electrical coupling to the stator. The adjustment motor optionally and preferably has a separate power source; any position controller and motor drive may optionally be used, having any type of power source. Preferably the amount of power required for management and control of the voltage output is relatively low as compared to the output of the generator itself.

The term "intermittent energy source" refers to any source of energy which fluctuates in terms of its availability. The term "constant electrical output" means an alternating or direct current output signal that has a constant peak voltage.

According to some embodiments, the controller for determining the loop length includes a voltage regulation system that receives rotation speed information from the speed sensor and determines the required loop length to provide the required voltage of the output signal for the generator.

The required loop length is optionally and preferably determined by a loop length regulation system. More preferably the loop length regulation system preferably determines the magnitude of the loop length in response to a relationship between the rotation speed and a peak voltage of the voltage of the output signal. Preferably, the loop length regulation system receives rotation speed information from the speed sensor and a requested peak voltage of the output signal and determines a magnitude of a loop length.

Preferably, the system includes a speed sensor that generates digital rotation speed information regarding the rotation speed of the shaft. However, if the system features an analog rotation speed sensor, then the voltage regulation system more preferably includes: an analog to digital converter that converts analog rotation speed information to digital rotation speed information (regarding the speed of the shaft), in order for the rotation speed information to be used. Optionally the voltage regulation system may operate with rotation speed information from an analog rotation speed sensor, without the analog to digital converter.

Preferably, the voltage regulation system further comprises a low pass filter for filtering the digital rotation speed information to provide filtered rotation speed information; and a processor, for determining the loop length in response to the filtered digital rotation speed information and to a relationship between the rotation speed and a peak voltage of the voltage of the output signal. Optionally and alternatively, the low pass filter is provided by hardware and/or is embedded in another component of the system, for example the rotation speed sensor itself. Also optionally, the rotation speed sensor is analog, in which case optionally an analog low pass filter may be used (for example in combination with the sensor or as a separate component).

In some embodiments, wherein the loop length is determined by the relative location of the stator and the rotor, the voltage regulation system further comprises a digital to analog converter, for converting a digital control signal outputted from the processor to a position control unit that controls this relative location. More preferably, the position control unit controls the position of the stator with respect to the rotor.

According to some embodiments, the shaft is rotated by a mechanical input element that is powered by a renewable energy source. Optionally and preferably, the renewable energy is selected from a group consisting of wind, water, solar and geothermal. More preferably, the system further includes a mechanical input element that rotates the rotor.

According to some embodiments, the system further includes a cooling fan that communicates with the shaft. Preferably, the controller controls the magnetic loop length of a generator so as to maintain a peak voltage of the output substantially constant despite changes in the rotation speed.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in order to provide what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice. In the drawings:

FIGS. IA- 1C show an exemplary, illustrative first embodiment of a generator system according to the present invention;

FIG. 2 is of an exemplary, illustrative method according to the present invention for control of the operation of the generator of Figure 1; FIG. 3 is of an exemplary, illustrative more detailed method according to the method of Figure 2;

FIG. 4 is a schematic block diagram of an illustrative system according to the present invention for generation of a constant level of voltage by a generator that is at least partially powered by a renewable energy source or "natural" energy; FIG. 5 A shows a second, exemplary, illustrative, non-limiting embodiment of a generator system according to the present invention, while

FIG. 5B is a flowchart of an exemplary, illustrative, non-limiting method of operation; FIG. 5C shows an exemplary, illustrative, non-limiting embodiment of switching system;

FIG. 6 shows the exemplary, illustrative embodiment of a generator system of Figure 1 with an optional wind turbine according to some embodiments of the present invention;

FIG. 7 is a flowchart of an exemplary, illustrative method for operating the system of Figures 1 or 6; and

FIG. 8 is a flowchart of another exemplary, illustrative method for operating the system of Figures 1 or 6 and 5 A.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is of a system and device for providing constant voltage power by a generator, through control of the length (preferably the effective length) of the stator and/or rotor winding of the generator. The length of the stator and/or rotor winding is controlled according to the rotational speed of the shaft of the generator, such that variations of the rotational speed of the shaft are compensated by changes to the effective length of the stator and/or rotor winding. The generator may optionally be an AC or DC generator.

The length of the stator and/or rotor winding which is changed is preferably the effective length, which more preferably is determined according to the position of the stator winding relative to the rotor winding. The length may optionally and preferably be adjusted continuously, according to a first embodiment of the present invention; or alternatively and optionally, may be adjusted discretely according to a second embodiment of the present invention. The present invention may optionally be used with any type of mechanical power source, and is useful with regard to any mechanical power input source which is characterized by variability. Examples of such mechanical power input sources include but are not limited to any type of renewable or "natural" energy source, including but not limited to wind, water, solar or geothermal. According to optional but preferred embodiments of the present invention, rather than providing a constant voltage output, optionally the effective length of the stator and/or rotor winding of the generator is controlled according to some criterion, such as a set point for example. The set point may optionally be a minimal required set point or a maximal permitted set point for the voltage output, and/or a within a range of permitted set point values.

The principles and operation of the present invention may be better understood with reference to the drawings and the accompanying description.

Referring now to the drawings, Figures IA- 1C show an exemplary, illustrative generator system 100 for generating a constant level of voltage of the output signal. The same reference numbers are used in all three drawings as the same components are shown. Generator system 100 features a connection to a mechanical power from a power source (not shown), which causes a shaft 106 of a generator 108 to rotate. Generator 108 is preferably a three phase, double winding generator, and features a rotor 110 and a stator 112. Rotor 110 preferably features rotor winding 114 while stator 112 preferably features stator winding 116.

The effective length of stator winding 116 relative to rotor 110 is preferably variable; more preferably for the exemplary embodiment of Figure 1, the effective length is continuously variable. In order to adjust the effective length of stator winding 116, stator winding 116 is preferably displaceable in the axial direction with respect to rotor 110. More preferably, stator winding 116 has a range of potential positions from a minimum displacement 126 (marked as position "X" in the drawing) to a maximum displacement 128 (marked as position "X-ΔX" in the drawing; it should be noted in this drawing that the displacement is measured from the right most end of the stator winding). At the minimum displacement 126, generator 108 provides a voltage of the output signal of Y volts while shaft 106 is at a rotation speed of n_min RPM. At the maximum displacement 128, generator 108 provides the same voltage Y but at a rotation speed for shaft 106 of n_max RPM. If the rotation speed does not exceed the minimal level, then the voltage of the output signal will not reach the required level. If the speed is above the maximal level, heat is generated and generator system 100 may overheat; however, this possibility may be prevented by adding a safety system which would prevent generator system 100 from operating if the shaft speed exceeds a certain level and/or if power generation exceeds a certain level. For each rotation speed of shaft 106 between the minimum and maximum RPM, an appropriate position of stator winding 116 is preferably determined such that the same voltage Y is always provided.

Without wishing to be limited by a single hypothesis, it is possible to consider the maximum displacement 128 of stator winding 116 as reducing the efficiency of coupling between stator winding 116 and rotor winding 114 through the magnetic field, by providing the shortest effective length of stator winding 116. This reduced efficiency enables the voltage Y of the output signal to be provided with a high rotation speed of shaft 106, which might otherwise be expected to provide a higher voltage of the output signal. By contrast, the minimum displacement 126 of stator winding 116 may be considered as providing the highest efficiency of coupling between stator winding 116 and rotor winding 114 through the magnetic field, by providing the longest effective length of stator winding 116. This increased efficiency enables the voltage Y to be provided with a low rotation speed of shaft 106, which might otherwise be expected to provide a lower voltage output. Stator winding 116 may optionally and preferably be moved (displaced) according to any suitable means for causing such movement. Preferably, as shown, stator winding 116 is moved by using a linear actuator 122 driven by a motor 124. Linear actuator 122 and motor 124 may optionally be combined in a single unit, for example as for a linear motor. Alternatively, linear actuator 122 may optionally comprise a hydraulic actuator and/or an electro-mechanical actuator. Motor 124 may optionally comprise any such motor of suitable power, such as for example an electric motor. Linear actuator 122 could be any type of linear motion device, including but not limited to a pneumatic cylinder device, hydraulic cylinder device, rack and pinion device, lead screw device and so forth. A rotation speed sensor 134 is preferably connected to shaft 106, for sensing the speed of rotation of shaft 106. Rotation speed sensor 134 may optionally feature any suitable speed sensing device, including but not limited to a shaft encoder, resolver, tachometer, a Hall effect sensor or any type of proximity sensor that reads the motion of a mark point on the perimeter of shaft 106. The mark point may be any type of marking, including but not limited to, a notch, screw or hole. Also optionally, a low pass filter may be combined with rotation speed sensor 134 and/or alternatively may optionally be a separate part of generator system 100 (for example as part of voltage regulation system 136 described below). A voltage regulation system 136 is electrically connected to rotation speed sensor 134 and to electrical motor 124. Voltage regulation system 136 is preferably PLC (programmable logic controller) based, although any type of programmable or computational device, or digital circuit, or any device featuring software, firmware or hardware, or a combination thereof, could also optionally be used. Generator system 100 preferably operates as follows. Mechanical power (not shown) is supplied to shaft 106 of generator 108, causing shaft 106 to rotate. Rotation speed sensor 134 senses the speed of rotation of shaft 106. This information is fed to voltage regulation system 136, which controls electric motor 124 (and hence linear actuator 122) in order to control the location of stator winding 116. Voltage regulation system 136 optionally and preferably operates by comparing the actual rotation speed of shaft 106 to the nominal speed, which is preferably predetermined. The nominal speed may optionally be considered as the expected setpoint speed of rotation for optimum efficiency of operation of generator 108. The nominal speed is preferably determined by testing generator 108 on a test bench, for example by connecting shaft 106 to a motor having variable speeds and testing the voltage of the output signal. If the actual, measured rotation speed is higher than the nominal speed, stator winding 116 is moved in the axial direction such that a lower portion of stator winding 116 may couple with the magnetic field (ie toward position 128 in Figure 1). If however the actual, measured rotation speed is lower than the nominal speed, stator winding 116 is moved in the opposite axial direction such that a higher portion of stator winding 116 may couple with the magnetic field (ie toward position 126 in Figure 1). The linear motion (and hence operational location) of stator winding 116 is preferably determined by the equation:

ΔS=X₀+(n-n₀)XΔX/(n_max-n_inin) In which: ΔX is the final axial position of stator winding 116.

Xo is axial position of stator winding 116 when shaft 106 is rotated at the nominal speed of the generator 108. n is the actual rotation speed of shaft 106. n₀ is the nominal speed of the generator 108. ΔS is the total axial stroke of stator 112. n_max is the maximal operation speed of generator 108 which is the maximal allowable shaft rotation speed. n_min is the minimal operation speed of generator 108 which is the minimum required shaft rotation speed. Figures IA- 1C show stator winding 116 in different positions, such that minimum displacement 126 (marked as position "X" in the drawing) and maximum displacement 128 (marked as position "X-ΔX" in the drawing) are different for the three drawings. The minimal displacement possible for this exemplary embodiment is shown in Figure IB, while the maximal displacement possible is shown in Figure 1C. An intermediate displacement is shown in Figure IB. All three drawings show exemplary displacements for the purpose of illustration only and without any intention of being limiting.

The location of stator winding 116 is optionally and preferably determined by voltage regulation system 136 according to a method shown in Figure 2. Figure 2 is of an exemplary, illustrative method according to the present invention for control of the operation of the generator of Figure 1. As shown, in stage 1 , the actual shaft speed of the generator shaft is measured by the shaft speed sensor. In stage 2, the voltage regulation system compares the actual shaft speed to the nominal shaft speed. In stage 3, the voltage regulation system controls length of stator windings according to this speed comparison in order for the generator to provide a constant voltage output. Preferably, the length is the effective length which is more preferably determined according to the relative location of the stator windings to the rotor windings. Stages 1-3 are then repeated at least once. Preferably, initially the voltage of the output signal is measured in relation to the rotation speed in order to define the control voltage curve_for a particular generator. Once this curve has been established for the generator, it is used for performing the above method for stage 3 as described above.

Figure 3 is a more detailed but still schematic diagram of a voltage regulation system according to the present invention. In stage 1, the control curve for the winding length required for a given rotation speed and desired output is determined for each generator system, preferably during system integration. This stage is not necessarily repeated once the system is operational. The method for determining the control voltage curve may optionally also be used for changing the "set point" of the output signal of the generator. For example, such a method could optionally be used to increase or decrease the level of voltage of the output signal to be provided by the generator. Optionally, increasing or decreasing the peak voltage of the output signal could be useful under a variety of circumstances, for example if the level of input mechanical power to the generator were to change. As described in greater detail below, such changes of input mechanical power may occur with regard to any type of energy source, but may be particularly prevalent with regard to renewable energy sources such as wind power or other types of "natural" energy sources. Preferably, such increasing or decreasing the level of voltage of the output signal is performed for any mechanical power input source which is characterized by variability. Stages 2-5 are preferably repeated at least once and are more preferably performed continuously as necessary, as a loop. In stage 2, the generator is operational and the generator's shaft is rotating. In stage 3, rotational speed of the shaft is measured by the rotational speed sensor as described in Figure 1. In stage 4, using the rotational speed of the shaft and the control voltage curve, the relative length of the windings is determined. Optionally and more preferably, the relative length is determined according to the location of the stator windings or rotor windings. Optionally and most preferably the relative location of the stator windings is determined, relative to the rotor windings. It should be noted that by "location" it is meant the effective location within the magnetic field. In stage 5, the (stator and/or rotor) windings are moved to the appropriate location; again it should be noted that the windings are optionally not "moved" physically but rather the location of the electrical coupling to the windings is altered, thereby altering the amount of voltage of the output signal. Figure 4 is a schematic block diagram of an illustrative system according to the present invention for generation of a constant level of voltage by a generator that is at least partially powered by a renewable energy source or "natural" energy. As shown, a system 400 features a mechanical power source 402, which is preferably a device powered by some type of renewable energy source or "natural" energy, optionally and preferably selected from the group consisting of wind, solar, water and geothermal. System 400 also preferably features a generator system 404, which may for example be implemented as described with regard to Figures 1 and/or 2 and/or 3.

Mechanical power source 402 is mechanically connected to a shaft 406 of a power generator 408 which is part of generator system 404, thereby causing shaft 406 to rotate. Mechanical power source 402 is optionally and preferably a variable power source, in the sense that the output level of mechanical power may optionally be variable. Such variation causes variation in the speed of rotation of shaft 406. However, a voltage regulation system 410 of generator system 404 controls the location of the stator windings in power generator 408, such that generator system 404 provides an (AC or DC) output signal that has a peak voltage that is maintained in a constant level, regardless of any variation of the speed of rotation of shaft 406.

Among the many advantages of the exemplary embodiment of the present invention shown in Figure 4 is that the provision of a constant peak voltage of the output signal may be made without altering or affecting the structure or function of the wind, water (hydroelectric), solar, geothermal or other type of turbine. Therefore, the function and design of the turbine itself may be selected for most effective capture of energy from the renewable energy source. No background art reference teaches or suggests such a system or device for generating a constant level of voltage of the output signal from a renewable energy source.

Figures 5A-5C show a second exemplary, illustrative embodiment of a generator system according to the present invention. This embodiment may optionally operate with and/or according to the aspects of the present invention illustrated in Figures 2-4. Figure 5 A shows an exemplary, illustrative generator system 500 for generating a constant level of voltage of the output signal. Generator system 500 features a connection to a mechanical power from a power source (not shown), which causes a shaft 506 of a generator 508 to rotate. Generator 508 is preferably a three phase, double winding generator, and features a rotor 510 and a stator 512. Rotor 510 preferably features rotor winding 514 while stator 512 preferably features stator winding 516.

The effective length of stator winding 516 relative to rotor winding 514 is preferably variable; more preferably for the exemplary embodiment of Figure 5, the effective length is discretely variable, such that a plurality of specific lengths may be optionally and preferably provided. In order to adjust the effective length of stator winding 516, stator winding 516 is not physically displaced; rather the location of an electrical coupling is selected from a plurality of potential positions 518, preferably ranging from a minimum position 526 (marked as position "X" in the drawing) to a maximum position 528 (marked as position "X-ΔX" in the drawing). At the minimum position 526, generator 508 provides voltage of Y volts while shaft 506 is at a rotation speed of n_min RPM, while at the maximum position 528, generator 508 provides the same voltage Y but at a rotation speed for shaft 506 of n_max RPM. For each rotation speed of shaft 506 between the minimum and maximum RPM, an appropriate position 518 of the electrical coupling to stator winding 516 from the plurality of available positions 518 is preferably determined such that the same or at least a sufficiently similar voltage Y (more preferably within a given range of tolerance for deviation from the value Y) is provided; preferably position 518 is selected such that voltage Y is the same or lower than the desired voltage of the output signal. Without wishing to be limited by a single hypothesis (and as described above for Figure 1), it is possible to consider the maximum position 528 of stator winding 516 as reducing the efficiency of coupling between stator winding 516 and rotor winding 514 through the magnetic field, by providing the shortest effective length of stator winding 516. This reduced efficiency enables the voltage Y to be provided with a high rotation speed of shaft 506, which might otherwise be expected to provide a higher voltage output. By contrast, the minimum position 526 of stator winding 516 may be considered as providing the highest efficiency of coupling between stator winding 516 and rotor winding 514 through the magnetic field, by providing the longest effective length of stator winding 516. This increased efficiency enables the voltage Y to be provided with a low rotation speed of shaft 506, which might otherwise be expected to provide a lower voltage output.

A rotation speed sensor 534 is preferably connected to shaft 506, for sensing the speed of rotation of shaft 506. Rotation speed sensor 534 may optionally feature any suitable speed sensing device, including but not limited to a shaft encoder, resolver, tachometer, a Hall effect sensor or any type of proximity sensor that reads the motion of a mark point on the perimeter of shaft 506. The mark point may be any type of marking, including but not limited to, a notch, screw or hole.

A voltage regulation system 536 is electrically connected to rotation speed sensor 534 and to a switching system 524. Voltage regulation system 536 is preferably PLC (programmable logic controller) based, although any type of programmable or computational device, or digital circuit, or any device featuring software, firmware or hardware, or a combination thereof, could also optionally be used. Switching system 524 preferably causes the electrical coupling to stator winding 516 to have one of the plurality of available positions 518 (switching system 524 is shown in more detail in Figure 5C).

A generator system 500 preferably operates as follows. Mechanical power (not shown) is supplied to shaft 506 of generator 508, causing shaft 506 to rotate. Rotation speed sensor 534 senses the speed of rotation of shaft 506. This information is fed to voltage regulation system 536, which controls switching system 524 in order to control the location of the electrical coupling to stator winding 516.

Voltage regulation system 536 optionally and preferably operates by comparing the actual rotation speed of shaft 506 to the nominal speed, which is preferably predetermined. The nominal speed may optionally be considered as the expected setpoint speed of rotation for optimum efficiency of operation of generator 508. If the actual, measured rotation speed is higher than the nominal speed, the effective coupling length of stator winding 516 is altered such that a lower portion of stator winding 516 causes electricity to be generated (ie toward position 528 in Figure 5). If however the actual, measured rotation speed is lower than the nominal speed, the effective coupling length of stator winding 516 is altered in an opposite manner (ie toward position 526 in Figure 1).

As a plurality of discrete positions 518 are available for stator winding 516, the actual rotational speed of shaft 506 is compared to a set of rotational speed values ω₀- ω_n, which in turn generate an Emf of Y volts, according to one of discrete positions 518 marked as X₀-X_n respectively. Upon measuring the rotation speed, switching system 524 activates the relay to move the electrical coupling with stator winding 516 to the position 518 which correlates to the selected rotation speed that is just below the actual measured rotation speed (thereby preferably obtaining Y or less than Y output volts).

The linear motion (and hence operational location) of stator winding 516 is preferably determined by the equation:

ΔS=Xo+(n-no)ΔX/(n_max-n_min) In which:

ΔX is the final axial position of the electrical coupling to stator winding 516. Xo is axial position of the electrical coupling stator winding 516 when shaft 506 is rotated at the nominal speed of generator 508. n is the actual rotation speed of shaft 506. n₀ is the nominal speed of generator 508. ΔS is the total axial stroke of stator 512. n_max is the maximal shaft rotation speed of generator 508. n_min is the minimal shaft rotation speed of generator 508.

Figure 5B is a flowchart of an exemplary, illustrative, non-limiting method of operation of the system of Figure 5 A. As shown, in stage 1, the speed of the rotation of the shaft of the generator (ω) is measured by a rotation speed sensor. The required loop length (L) is determined according to the pre-determined curve for the generator, in which the loop length is plotted according to rotation speed, in stage 2. It should be noted that the curve may optionally be in any form, such as a table of a plurality of values, a graphical curve, an equation or equations, and so forth, as long as the correct or desired loop length may be selected according to the rotation speed. Next, in stage 3, the loop length is preferably determined by coupling the stator electrically at a position Xn to provide a loop length preferably as close as possible to the optimal required loop length, more preferably to provide the desired voltage or a voltage as close as possible to the desired voltage. Such a change in loop length then causes the voltage of the output signal of the generator to be changed due to the loop length changes, in stage 4. Stages 1-4 are then optionally and preferably repeated at least once and are more preferably repeated periodically, most preferably as necessary, for example according to the changes in the rotation speed of the shaft, such that the stages are preferably repeated with a frequency sufficient to compensate for the changes in rotation speed.

Figure 5C shows the switching system of Figure 5A in more detail (numbered as switching system 524). As shown, switching system 524 includes a plurality of solid state relays 551, 557, 560 and 563. The output lines 555, 559, 562 and 565 of solid state relays 551, 557, 560 and 563, respectively, are connected to the generator's stator windings (not shown). The control lines 553, 558, 561 and 564 of solid state relays 551, 557, 560 and 563, respectively, are connected to the outputs of the voltage regulation system (not shown), in order for the voltage regulation system to be able to select one of solid state relays 551, 557, 560 or 563 for operation. The control output line 554 of solid state relays 551, 557, 560 and 563 is grounded by a ground 556. In operation, according to the rotation speed of the shaft (not shown), the voltage regulation system couples the stator electrically at a position selected from XO...Xn to provide a loop length preferably as close as possible to the optimal required loop length. In order for such coupling to occur, the voltage regulation system operates a selected one of the plurality of solid state relays 551, 557, 560 or 563 by operating a selected control line 553, 558, 561 or 564, respectively, thereby switching the selected relay and causing the generator's output signal voltage line 552 to be connected to one of the generator's stator windings XO... Xn (not shown) through one of output lines 555, 559, 562 or 565, respectively, thus connecting the required stator winding point of contact to create the required winding length. Figure 6 shows the exemplary, illustrative embodiment of an generator system of Figure 1 with an optional wind turbine according to some embodiments of the present invention.

As shown, an exemplary, illustrative generator system 600 for generating a constant level of voltage a shaft coupling 644 to a mechanical power from a wind driven power source 646, which causes a shaft 606 of a generator 608 to rotate. Generator 608 is preferably a three phase, double winding generator, and features a rotor 610 and a stator 612. Rotor 610 preferably features rotor winding 614 while stator 612 preferably features stator winding 616. The effective length of stator winding 616 relative to rotor 610 is preferably variable; more preferably for the exemplary embodiment of Figure 6, the effective length is continuously variable. In order to adjust the effective length of stator winding 616, stator winding 616 is preferably displaceable in the axial direction with respect to rotor 610. More preferably, stator winding 616 has a range of potential positions from a minimum displacement 626 (marked as position "X" in the drawing) to a maximum displacement 628 (marked as position "X-ΔX" in the drawing; it should be noted in this drawing that the displacement is measured from the right most end of the stator winding). At the minimum displacement 626, Generator 608 provides voltage of Y volts while shaft 606 is at a rotation speed of n_mm RPM. At the maximum displacement 628, Generator 608 provides the same voltage Y but at a rotation speed for shaft 606 of n_max RPM. If the rotation speed does not exceed the minimal level, than the voltage of the output signal will not reach the required level. If the speed is above the maximal level, heat is generated and generator system 600 may overheat; however, this possibility may be prevented by adding a safety system which would prevent generator system 600 from operating if the shaft speed exceeds a certain level and/or if power generation exceeds a certain level. For each rotation speed of shaft 606 between the minimum and maximum RPM, an appropriate position of stator winding 616 is preferably determined such that the same voltage Y is always provided. Generator system 600 preferably operates in a similar if not identical manner to the system of Figure 1.

As shown, stator winding 616 may optionally and preferably be moved (displaced) according to any suitable means for causing such movement. Preferably, as shown, stator winding 616 is moved by using a linear actuator 622 driven by a motor 624. Linear actuator 622 and motor 624 may optionally be combined in a single unit, for example as for a linear motor. Alternatively, linear actuator 622 may optionally comprise a hydraulic actuator and/or an electro-mechanical actuator. Various alternatives and options for linear actuator 622 and motor 624 may optionally be as discussed for Figure 1. A rotation speed sensor 634 is preferably connected to shaft 606, for sensing the speed of rotation of shaft 606, optionally as discussed for Figure 1.

A voltage regulation system 636 is electrically connected to rotation speed sensor 634 and to electrical motor 624. Voltage regulation system 636 is preferably PLC (programmable logic controller) based, although any type of programmable or computational device, or digital circuit, or any device featuring software, firmware or hardware, or a combination thereof, could also optionally be used.

Generator system 600 preferably operates as described in Figure 1, with the additional detailed description of the source of mechanical power, which is wind driven power source 646. Wind driven power source 646 preferably features at least one if not a plurality of blades 640 as shown, and a speed reducer 642. As blades 640 rotate, the rotational energy transferred through shaft coupling 644 causes shaft 606 to rotate. Speed reducer 642 may optionally be implemented as gears which are known in the art, but are optionally and preferably implemented as fixed ratio transmission. Speed reducer 642 for implementation with some embodiments of the present invention as shown does not require variable ratio transmission. Speed reducer 642, shaft coupling 644 and blades 640 could all optionally be implemented as known in the art by one of ordinary skill in the art.

Figure 7 is a flowchart of an exemplary, illustrative method for operating the system of Figures 1 or 6. As shown, in stage 1, the speed of the rotation of the shaft of the generator (ω) is measured by a rotation speed sensor. The required loop length (L) is determined according to the pre-determined curve for the generator, in which the loop length is plotted according to rotation speed, in stage 2. It should be noted that the curve may optionally be in any form, such as a table of a plurality of values, a graphical curve, an equation or equations, and so forth, as long as the correct or desired loop length may be selected according to the rotation speed.

Next, in stage 3, the loop length is preferably determined by moving the stator in an axial direction (with respect to the rotor), such that the stator is preferably displaced with regard to the rotor, to provide an overlap according to the required loop length. Such a change in loop length then causes the voltage of the output signal of the generator to be changed due to the loop length changes, in stage 4. Stages 1-4 are then optionally and preferably repeated at least once and are more preferably repeated periodically, most preferably as necessary, for example according to the changes in the rotation speed of the shaft, such that the stages are preferably repeated with a frequency sufficient to compensate for the changes in rotation speed.

Figure 8 is a flowchart of another exemplary, illustrative method for operating the system of Figures 1 or 6 in combination with the electrical switching of Figure 5B. For this method, the loop length is preferably determined first coarsely and is then fine tuned. Stages 1 and 2 are performed as for Figure 7. In stage 3, the loop length is preferably determined by coupling the stator electrically at a position Xn to provide a voltage of the output signal as close as possible to the required voltage. This stage provides a coarse determination of the loop length. In stage 4, the loop length is preferably fine tuned by changing the relative position of the stator and the rotor, preferably by moving the stator axially with regard to the rotor. In stage 5, the change in loop length then causes the voltage of the output signal of the generator to be changed due to the loop length changes. Stages 1-5 are then optionally and preferably repeated at least once and are more preferably repeated periodically, most preferably as necessary, for example according to the changes in the rotation speed of the shaft, such that the stages are preferably repeated with a frequency sufficient to compensate for the changes in rotation speed. While the invention has been described with respect to a limited number of embodiments, it will be appreciated that many variations, modifications and other applications of the invention may be made.

Claims

What is claimed is:

1. A generator system for providing a signal output having a constant voltage, comprising: a. A generator for generating the output signal, the generator comprising a shaft for being rotated and a winding; b. A speed sensor for sensing a rotational speed of said shaft; c. A controller for controlling an effective length of said winding of the generator according to said speed.

2. The generator system of claim 1, comprising a stator and a rotor, wherein said winding comprises stator winding, rotor winding or a combination thereof.

3. The system of claims 1 or 2, wherein said controller further comprises: An adjustment motor for controlling an effective length of said winding; and

A voltage regulator for regulating said adjustment motor according to said speed of said shaft.

4. The system of claim 3, wherein said adjustment motor physically moves said stator relative to said rotor.

5. The system of claims 1 or 2, wherein said controller further comprises a switch for controlling an effective length of said winding by electrically coupling said stator winding at a selected position.

6. The system of any of claims 3-5, wherein said controller comprising said switch and said adjustment motor.

7. The system of any of claims 1-6, wherein said shaft of said generator is adapted for being rotated by a mechanical power input source characterized by variability.

8. The system of claim 7, wherein said mechanical power input source is powered by a renewable energy source.

9. The system of claim 8, wherein said renewable energy is selected from the group consisting of wind, water, solar and geothermal.

10. The system of any of claims 1-9, wherein said generator comprises an AC generator or a DC generator.

11. A method for generating energy from an intermittent energy source, comprising:

Rotating a shaft of a generator with energy from the intermittent energy source;

Measuring a speed of rotation of said shaft;

Controlling a length of a winding of the generator according to said speed of rotation, thereby providing a constant voltage output from the intermittent energy source.

12. The method of claim 11, wherein said winding comprises stator winding, rotor winding or a combination thereof.

13. The method of claim 12, wherein said length is an effective length of said stator winding relative to a rotor winding.

14. The method of claim 13, wherein said effective length is adjusted continuously according to an axial position of said stator winding relative to said rotor winding.

15. The method of claim 13, wherein said effective length is adjusted according to an electrical connection to said stator winding, wherein said electrical connection is selected from a plurality of available axial positions.

16. The method of claim 13, wherein said effective length is adjusted continuously according to an axial position of said stator winding relative to said rotor winding, wherein said axial position is selected from a plurality of available axial positions.

17. The method of any of claims 13-16, wherein said effective length is adjusted according to said electrical connection and according to said axial position of said stator winding.

18. The method of any of claims 11-17, wherein said generator comprises an AC generator or a DC generator.

19. A method for generating energy from an intermittent energy source, comprising:

Rotating a shaft of a generator with energy from the intermittent energy source; Measuring a speed of rotation of said shaft; and

Controlling a length of a winding of the generator according to said speed of rotation.

20. The method of claim 19, wherein said winding comprises a stator winding, a rotor winding or a combination thereof.

21. The method of claims 19 or 20, wherein said generator comprises an AC generator or a DC generator.