KR20090127428A - System and method for generating an alternating current output signal - Google Patents

Abstract

A system and device for providing AC signal. The system includes: an AC generator that outputs an AC output signal and includes an AC rotor that communicates with a shaft that is rotated at a rotation speed; a speed sensor for sensing the rotation speed; and a controller for controlling a magnetic field of the AC generator in response to the rotation speed; wherein the controller comprises a direct current (DC) generator that generates a current that is provided to the AC generator so as to control the magnetic field of the AC generator.

Description

SYSTEM AND METHOD FOR GENERATING AN ALTERNATING CURRENT OUTPUT SIGNAL}

Related Applications

This application claims priority from US Provisional Application No. 60 / 907,248, filed March 27, 2007, and is incorporated herein by reference, as set forth in its entirety.

FIELD OF THE INVENTION The present invention relates to systems and apparatus for generating electricity at a constant output, potentially with variable speeds, and more particularly to systems and apparatuses characterized by voltage fluctuation systems.

Generating electricity through the use of electric generators is important in modern life. These generators require an external energy source to operate, for example, various types of fossil fuels and / or renewable energy. The generator then consumes an energy source to generate electricity. However, it is important that the power output is constant so that the generated electricity is used.

The power output may be constant if the shaft speed of the generator is constant. However, the shaft speed of the generator cannot always be maintained at a constant rate. Therefore, the various generators maintain at least the minimum speed, so that the power output provided is determined according to the minimum speed of the shaft. If the shaft speed is increased above the minimum, the generated excess power is discarded and wasted.

Various solutions have been tried, but none completely solve the problem for AC generators. For example, US Pat. No. 5,414,83 provides a method of controlling a direct current (DC) motor or generator, particularly a direct current (DC) motor or generator having a permanent magnet type. Due to the functional difference between the AC generator and the DC generator, the above-mentioned solution does not work for the AC generator.

US patent application 2004/0257050 describes a method and apparatus for generating a constant current, wherein the US patent application overcomes the drawbacks potentially associated with variable shaft speed through controlling the current output by a generator, The level of the current was made constant. Therefore, the described invention relates to relatively complex current stabilization.

Various solutions to achieve a stabilized voltage output use inertia or friction to control shaft speed variations; Use torque control to control shaft speed; Or converting varying AC electricity to DC electricity, and converting DC electricity back to a standard grid AC power source. All of these methods obviously waste very energy.

In order to use a renewable energy source, systems and apparatuses include wind used in wind turbines; The sun used in solar panels; Hydraulic power such as tidal power; Has been using "natural" energy. Wind energy can be particularly variable because of the tendency for wind to increase and decrease power and / or to change direction very regularly. However, all "natural" energy sources can destabilize power levels. Thus, in renewable energy, the ability to convert unstable mechanical power into stable power is greatly demanded in various applications.

Various solutions have been proposed in this area to overcome instability of renewable energy sources, in particular for wind generation. For example, US patent 7070615 provides a solution to wind power by adjusting the magnetic field according to the rotational speed of the wind turbine in accordance with the feedback determined by measuring the output voltage or current. US patent application 2004/0119292 provides a method of controlling the shaft speed of a generator by controlling the turbine of the generator, as noted above, which is disadvantageous as a solution. The presented method further requires a diode rectifier for operation, which is another disadvantage.

U.S. Pat.No.5083039 controls the power output by controlling the stator current, thereby controlling the magnetic field of the generator. However, a change in the stator current causes a change in the generator torque. To compensate for changes in torque, the shaft speed is controlled by varying the turbine's "wings" or the pitch of the blades, which can be disadvantageous due to wind conditions and require additional consumption of energy. It may be disadvantageous in some cases. Similarly, US Pat. No. 6,137,187 has the disadvantage of requiring a pitch control system.

The term "constant electrical output" means an alternating output signal having a constant peak voltage.

The present invention provides a system and method for sensing the rotational speed of a shaft rotating at a variable rotational speed and controlling the magnetic field of the AC generator in response to the detected speed. The control includes using a DC generator to supply current to the AC generator. This current determines the magnetic field of the AC generator. The magnetic field can be controlled in such a way that despite the change in the rotational speed of the shaft, the peak voltage of the output signal of the AC generator remains substantially constant.

The electromagnetic force induced in an AC generator is determined by Faraday's law:

here:

는 권선의 접선 속도(tangential speed)이다.EMF is the output voltage,

Is the tangential speed of the winding.

L is the length of the winding across the magnetic flux.

B is the magnetic field strength.

sin (θ) is the sine angle between the winding and the magnetic flux.

The above equation indicates that the peak voltage of the AC output signal of the AC generator depends on the shaft rotation speed and on the mechanical power used to rotate the shaft. If the level of mechanical power is variable, the shaft rotational speed is also variable. However, even if the shaft rotational speed varies, the peak voltage must remain substantially constant.

Therefore, the present invention does not require the shaft rotational speed to be constant and can be used in a wide variety of applications and includes power generating renewable or "natural" energy sources or several other energy sources with variable outputs. But not limited to. Instead, according to embodiments of the present invention, the measurement of the shaft rotational speed is used to control the magnetic field strength B through a feedback or control mechanism (including a DC generator) according to the rotational speed of the shaft, so that the constant voltage It provides constant voltage output and generates power stably.

According to embodiments of the present invention, the control of the magnetic field strength of the AC generator is preferably provided to the DC generator, the DC generator characterized by a rotor winding connected to the rotor winding of the AC generator. The rotational speed of the shaft of the AC generator is measured; According to this measurement, the operation of the DC generator is used to increase or decrease the magnetic field strength, so as to maintain the constant voltage output even if the rotational speed of the shaft changes. The DC generator optionally and preferably has a separate power source. Preferably, the amount of power required to control and manage the voltage output is relatively small compared to the output of the generator itself; For example, the test presented below indicates that the required control power is less than 30 W for a 5 KW generator. Optionally and preferably, the rotor windings of the DC generator are connected to the rotor windings of the AC generator in order to control the magnetic field of the AC generator.

A system for providing an alternating current (AC) output signal, the system comprising: an AC generator for outputting an AC output signal, the AC generator including a shaft that rotates at a rotational speed and a subsequent AC rotor; A speed sensor detecting the rotation speed; And a controller for controlling the magnetic field of the AC generator in response to the rotational speed, wherein the controller is configured to generate a direct current (DC) generator for generating a current provided to the AC generator to control the magnetic field of the AC generator. Include.

Conveniently, the DC generator includes a DC rotor following the shaft.

Conveniently, the DC rotor is connected to the AC rotor.

Conveniently, the DC rotor is connected to the AC rotor by rigid wiring.

Conveniently, the DC generator includes a DC stator supplied by an excitation voltage having an amplitude responsive to the rotational speed.

Conveniently, the controller includes a voltage regulation system that receives rotational speed information from the speed sensor and determines the amplitude of the excitation voltage provided to the DC generator.

Conveniently, the voltage change rate system determines the amplitude of the excitation voltage in response to the relationship between the peak voltage of the AC output voltage and the rotational speed.

Conveniently, the voltage rate change system comprises: an analog to digital (AD) converter for converting analog rotational speed information into digital rotational speed information; A low pass filter for filtering the digital rotation speed information to provide filtered rotation speed information; A processor for determining the excitation voltage in response to filtered digital rotation speed information and in response to a relationship between the peak voltage and the rotation speed of an AC output voltage; And a digital to analog (DA) converter for converting the digital control signal output from the processor into an analog signal for controlling the amplitude of the excitation voltage.

Conveniently, the system includes a speed sensor that generates digital rotational speed information.

Conveniently, the controller includes a voltage change rate system that receives rotational speed information and the requested peak voltage of the AC output signal from the speed sensor and determines the amplitude of the excitation voltage provided to the DC generator.

Conveniently, the shaft is rotated by a mechanical pressure element powered by a renewable energy source.

Conveniently, the renewable energy is selected from the group consisting of wind, water, sun and geothermal heat.

Conveniently, the system further includes a mechanical input element for rotating the rotor.

Conveniently, the system further comprises a cooling fan leading to the shaft.

Conveniently, the controller controls the magnetic field of the AC generator to keep the peak voltage of the AC output substantially constant despite the change in the rotational speed.

Unless defined otherwise, 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.

The invention is described herein by way of example only with reference to the accompanying drawings. With reference to the specific drawings in particular reference, specificities are presented merely for purposes of explanation of embodiments of the invention and in an exemplary manner, and provide that they can be most usefully and easily understood with the principles and conceptual aspects of the invention. Is presented for. Attempts are not made to present a more detailed structural description of the invention rather than the need for a basic understanding of the invention, and through the description with reference to the drawings, how some forms of the invention are substantially embodied. Will be apparent to those skilled in the art.

In the drawings:

1 illustrates an exemplary AC generator system, in accordance with the present invention;

2 presents a representative exemplary method in accordance with the present invention for control of the operation of the generator of FIG. 1;

3 is a more detailed but schematic diagram of a voltage rate variation system according to the present invention;

4 is a schematic block diagram of an exemplary system according to the present invention for generating a constant level of voltage by a generator at least partially powered by a renewable energy source or “natural” energy;

5 presents the results of a test of an exemplary system in accordance with the present invention;

6 is a view showing in more detail the voltage change rate system and the rotational speed sensor according to an embodiment of the present invention;

7 is a view showing in more detail the voltage fluctuation system and the rotational speed sensor according to an embodiment of the present invention;

8 is a view showing in more detail the voltage change rate system and the rotational speed sensor according to an embodiment of the present invention;

9 and 10 show the relationship between the rotational speed of the shaft and the control current for different values of the peak voltage of the AC output signal; And

11 shows a method according to an embodiment of the invention.

The present invention is a system and apparatus for providing a constant voltage power (an alternating current output signal having a substantially constant peak voltage) by an AC generator through control of the magnetic field strength of the AC generator, wherein the control uses a DC generator. . The magnetic field strength is controlled by the current supplied by the DC generator and in accordance with the rotational speed of the shaft of the AC generator, so that the change in the rotational speed of the shaft is compensated by the change in the magnetic field strength.

According to embodiments of the present invention, the DC generator is characterized by a rotor winding electrically connected to the rotor winding of the AC generator. The rotational speed of the shaft of the AC generator is preferably measured; According to this measurement, the operation of the DC generator is used to increase or decrease the magnetic field strength, so as to maintain the constant voltage output even if the rotational speed of the shaft changes.

Optionally and preferably, the rotor winding of the DC generator is connected to the rotor winding of the AC generator which controls the magnetic field of the AC generator.

The invention may optionally be used with several types of mechanical power sources, but may be useful for mechanical power input sources that are characterized by variability. Examples of such mechanical power input sources include, but are not limited to, various types of renewable or "natural" energy sources, including but not limited to wind, water, sun or geothermal energy.

In accordance with optional embodiments of the present invention, rather than providing a constant voltage output, rather, the magnetic field of the AC generator is optionally controlled according to criteria such as, for example, a set point. The set point may optionally be the minimum required set point or may be the maximum allowed set point for the voltage output and / or within the range of allowed set point values.

The principles and operation of the present invention may be easier to understand with reference to the drawings and the accompanying techniques.

Referring to FIG. 1, FIG. 1 is a representative example AC generator system 100 for generating a constant level of output voltage. The generator system 100 is characterized by a connection from a power source (not shown) to mechanical power that causes the shaft 106 of the AC generator 108 to rotate. The shaft 106 also features a cooling fan 104 that selectively cools the operation of the generator system 100. AC generator 108 is preferably a three phase, double winding generator, and features rotor 110 and stator 112. The rotor 110 preferably features the rotor windings 114, while the stator 112 preferably features the stator windings 116.

The auxiliary DC generator 118 is optionally and preferably installed on the shaft 106, as shown, to control the strength of the magnetic field of the AC generator 108. DC generator 118 features DC rotor 120 with DC rotor windings 122 and DC stator 124 with DC stator windings 126. DC rotor winding 122 is preferably connected to rotor winding 114 of AC generator 108 via connector 130 and preferably includes several types of windings, which may optionally be rigid windings, The DC rotor winding 122 rotates at the same speed as the rotor winding 114. DC stator winding 126 is connected to DC power source 128 via a suitable connector 132, as is known in the art.

Rotational speed sensor (also referred to as speed sensor) 134 is preferably connected to shaft 106 to sense the rotational speed of shaft 106. Rotational speed sensor 134 may optionally feature an appropriate speed sensing device and may be mounted on the periphery of shaft encoder, resolver, tachometer, hall effect sensor, or shaft 106. It includes, but is not limited to, several types of proximity sensors that read the movement of a mark point. Mark points include, but are not limited to, several types of markings, notches, screws, or holes.

The voltage change system 136 is electrically connected to the rotational speed sensor 134 and to the DC power source 128. Voltage fluctuation system 136 may optionally be used as several types of programmable or computationally demanding devices, or as digital circuitry, or devices featuring software, firmware, or hardware, or combinations thereof, Logic controller).

The AC generator system 100 preferably operates as follows. Mechanical power (not shown) is supplied to the shaft 106 of the AC generator 108 to rotate the shaft 106. The initial excitation voltage is induced by the DC power supply 128 to the DC stator 124 and causes the DC rotor 120 to be affected by an external magnetic field. In addition, the DC power supply 128 rotates the DC rotor 120. The combination produces an EMF in the DC generator 118, whereby a current (also referred to as a control current) flows from the DC rotor 120 to the rotor 110 of the AC generator 108 and at the rotor 110. Create a rotating magnetic field. As a result, the EMF is generated at the output of the AC generator 108 (ie, the AC generator 108 generates electricity).

Rotational speed sensor 134 senses the rotational speed of shaft 106. This information is supplied to a voltage drift rate system 136 that controls the DC power supply 128 to change the excitation voltage at the DC stator 124 to change the EMF output by the DC generator 118. In turn, this controls the magnetic field strength of the AC generator 108 by varying the current in the rotor winding 114.

The excitation voltage is optionally and preferably determined by the voltage gradient system 136 according to the method shown in FIG. 2. FIG. 2 presents a representative descriptive method according to the present invention with respect to the control of the operation of the generator of FIG. 1. As shown, in step 1, the actual rotational speed (also referred to as shaft speed) of the AC generator shaft is measured by the rotational speed sensor. In step (2), the voltage change rate system changes the value of the DC power supply control input, which preferably changes the excitation voltage of the DC stator. The two steps are then optionally and preferably repeated as necessary, but step (1) is repeated at least once.

Preferably, the output voltage is initially measured with respect to the rotational speed to define a control voltage curve for the particular generator. Once this curve is established for the generator, it is used to carry out the method described above.

Also, the method can optionally be used to change the "set point" of the output signal of the AC generator. For example, this method can optionally be used to increase or decrease the peak voltage of the output signal provided by the AC generator. Optionally, increasing or decreasing the peak voltage of the output signal can be used under various circumstances, for example when the level of inputting mechanical power to the AC generator is varied. As described in more detail below, this change in mechanical power input can occur for several types of energy sources, but especially for renewable energy sources such as wind or other types of "natural" energy sources. It can be done widely and generally. Preferably, increasing or decreasing the level of the output voltage is performed for a mechanical power input source characterized by variability.

3 is a diagram of a voltage rate change system according to the invention, which is more detailed but schematic. In step (1), as described above, the control voltage curve is determined for each generator system, preferably during system integration. This step need not be repeated if the system is running.

Steps 2 to 5 are preferably repeated at least once, preferably further successively as a loop if necessary. In step 2, the AC generator is operated and the shaft of the AC generator is rotated. In step 3, the rotational speed of the shaft is measured by the rotational speed sensor as described in FIG. 1. In step 4, using the rotational speed of the shaft and the control voltage curve, the amount of control voltage output is determined. In step 5, the control voltage is output by a control voltage output generator, which is preferably an associated DC generator, as shown in FIG.

4 is a schematic block diagram of an exemplary system according to the invention for generating a constant level of voltage by a generator at least partially powered by a renewable energy source or “natural” energy. As shown, the system 400 is a mechanical power source 402 which is optionally and preferably a device powered by various types of renewable or "natural" energy selected from the group consisting of wind, sun, water and geothermal energy. Is characterized by. In addition, the system 400 preferably features an AC generator system 404 that may be implemented, for example, as described with respect to FIGS. 1 and / or 2 and / or 3.

The mechanical power source 402 is mechanically connected to the shaft 406 of the AC generator 408, which is part of the AC generator system 404, causing the shaft 406 to rotate. The mechanical power source 402 can be selectively and preferably a variable power source in that the output level of the mechanical power can be selectively varied. Such a change causes a change in the rotational speed of the shaft 406. However, the voltage fluctuation system 410 of the AC generator system 404 controls the magnetic field in the AC generator 408, so that the AC generator system 404 is independent of the change in the rotational speed of the shaft 406, Provides an AC output signal with a peak voltage that is maintained at a constant level.

Among the many advantages of the exemplary embodiment of the present invention shown in FIG. 4, the provision of a constant peak voltage of the AC output signal alters or acts on the structure or function of wind, water (hydropower), solar, geothermal or other types of turbines. The advantage is that it can be done without. Therefore, the function and design of the turbine itself can be chosen to most effectively capture energy from the renewable energy source. There is no background reference presenting or suggesting such a system or apparatus that generates a constant level of output voltage from a renewable energy source.

Example 1

Example system testing

This example describes a test run on a non-limiting system that is representative of the exemplary embodiment in accordance with the present invention. Systems featuring hybrid, dual winding three phase generators include both DC and AC generators, ie, product number ECO3-2S4 (Mecc Alte S.p.A., Italy); And voltage fluctuation systems based on CQM-45 (Omron Inc., USA) programmable logic controller (PLC). The set point voltage of the system is 285 Vac. The AC generator is powered by an electric motor connected to a variable speed motor driver. Thereafter, the rotation speed of the AC generator shaft is changed in accordance with the speed of the motor. For each rotational speed, the excitation voltage of the auxiliary DC generator is changed until the peak voltage of the AC output reaches the set point value (285 Vac).

FIG. 5 shows auxiliary excitation voltage values of the DC generator according to the speed of the shaft of the AC generator in accordance with the requirement to maintain the constant voltage output by the AC generator.

6 illustrates a more detailed voltage rate variation system 136 and rotation speed sensor 134, in accordance with an embodiment of the present invention.

The rotational speed sensor 134 provides the analog rotational speed information to the analog to digital (AD) converter 161 which converts the analog rotational speed information into the digital rotational speed information. The digital rotational speed information is provided to a low pass filter 162 that filters the digital rotational speed information to provide filtered rotational speed information. The low pass filter 162 may apply a Fast Fourier Transformation filtering process, but this is not necessary.

Processors such as FPGA 164 determine excitation voltages in response to the filtered digital rotational speed information and in response to the relationship between the peak voltage of the AC output voltage and the rotational speed. Information indicative of this relationship may be stored in the FPGA, and the instructions executed by the FPGA may be stored in a memory unit, such as EPROM 165.

The processor 164 outputs a digital control signal indicating the determination to the digital to analog (DA) converter 166. The DA converter 166 converts the digital control signal into an analog control signal that controls the amplitude of the excitation voltage. The analog control signal is supplied to a current driver 168 that provides a current signal provided to the DC power supply 128 and determines the excitation voltage output by the power supply 128. The signal or analog control signal output to the current driver 168 can be measured by the voltage meter 171 and can be displayed on the display of the voltage meter. Multiplexer 169 or other sampling circuitry may be provided between the current driver 168 and the output port of the voltage gradient system 136, allowing for the provision of a current signal to the DC power supply 128, as well as for measurement. .

Conveniently, the DA converter 166 includes a potentiometer used to determine the output range of the DA converter 166, in particular the potentiometer outputs a zero voltage analog control signal.

The protocol converter 163 or another port or interface may be used to provide the peak voltage required for the voltage gradient system 136.

The port or interface (or additional port or interface) can be used to provide web based management, as shown in FIG. 8. The web-based management entity 175 of the voltage change rate system 136 allows data about the rotational speed measurement and / or the measurement of the analog signal output to the DC power 128 to be output to one or more external devices. And / or one or more interactions of the user with the voltage change system 136. The web-based management entity 175 may be software, firmware, hardware or a combination thereof.

Referring to FIG. 6, the voltage gradient system 136 may be mounted on a printed circuit board. Additionally or alternatively, it can be communicated with a web server (not shown) that can provide one or more web pages. These web pages act as an interface for the voltage gradient system 136 for the user, for example for simple configuration selection, as is known in the art.

The voltage change rate system 136 may output information to a display such as the rotational speed display 172 or a combination thereof as well as the display of the voltage meter 171. Information may be provided through a port or interface.

According to another embodiment of the present invention, the rotational speed sensor provides digital rotational speed information rather than analog rotational speed information. FIG. 7 shows a rotational speed sensor that includes an incremental encoder 134 ′. Incremental encoder 134 'generates digital rotational speed information, thereby eliminating the need for various components of voltage gradient system 136 (such as AD converter 161 and digital low pass filter 162). .

9 and 10 show the relationship between the rotational speed of the shaft and the control current for different values of the peak voltage of the AC output signal, and the curve in FIG. 10 corresponds to the values contained in the table of FIG. 9.

Many curves show the relationship between the rotational speed of the shaft and the control current for different peak voltages of the AC output signal.

11 illustrates a method 300 according to the practice of the present invention.

The method 300 is initiated by step 310 or by step 320.

Step 310 includes determining the requested peak voltage of the AC output signal output to the AC generator.

Step 320 includes receiving information indicative of the requested peak voltage of the AC output signal output by the AC generator.

Steps 310 and 320 are followed by step 330 of detecting the rotational speed of the shaft.

The method 300 includes rotating the shaft by a mechanical input element. This step is not presented for simplicity of explanation. The shaft can be rotated by a mechanical input element powered by a renewable energy source. Renewable energy may be a wind, water, solar or geothermal energy source.

Step 330 is followed by step 340 of controlling the magnetic field of the AC generator in response to the rotational speed.

According to various embodiments of the present invention, step 340 may comprise at least one or a combination of the following steps:

(Iii) determining (342) the amplitude of the excitation voltage provided to the DC stator of the DC generator in response to the relationship between the peak voltage and the rotational speed of the AC output voltage, the DC generator having a shaft and a subsequent DC rotor; Can be. The DC rotor may be connected to the AC rotor, but for example by a rigid winding. The amplitude can be determined such that the peak voltage of the AC output signal remains substantially constant despite the change in rotational speed.

(Ii) supplying a DC stator of the DC generator by an excitation voltage, 344, wherein the excitation voltage has an amplitude in response to the rotational speed.

(Iii) providing 346 a control current by a direct current (DC) generator to the AC generator; The control current responds to the amplitude of the excitation voltage. This control current controls the magnetic field of the AC generator.

Step 340 is followed by step 350 of outputting an AC output voltage by the AC generator. The peak voltage of the AC output signal responds to the magnetic field of the AC generator. The AC generator includes a shaft and a subsequent AC rotor.

Determining 342 may include at least one of the following steps or a combination thereof; (Iii) receiving (342) (1) rotational speed information from the speed sensor; (Ii) receiving the requested peak voltage of the AC output voltage (342) (2); And (iii) determining (342) (3) the amplitude of the excitation voltage in response to the relationship between the rotational speed of the shaft and the control current; (Iii) determining the amplitude of the excitation voltage in response to the relationship between the control current values, the rotational speed of the shaft and the requested peak voltage of the AC output voltage (342) (4).

Note that by changing the requested peak voltage of the AC output signal, the "set point" of the system is changed. When the peak voltage changes, the discrimination must select the relevant curve (or formula). Thus, step 344 may include selecting between curves, such as the curve shown in FIG. 10.

According to an embodiment of the invention, the determination is performed in the digital domain. As such, step 344 comprises: (i) converting analog rotational speed information into digital rotational speed information; (Ii) low pass filtering the digital rotational speed information to provide filtered rotational speed information; (Iii) determining the excitation voltage in response to the filtered digital rotational speed information and in response to the relationship between the peak voltage and the rotational speed of the AC output voltage; (Iii) generating a digital control signal responsive to said determining; And (iii) converting the digital control signal into an analog signal for controlling the amplitude of the excitation voltage.

The method 300 may include a step 370 of activating the cooling fan that follows the shaft. The cooling fan is activated by the shaft. The method 300 may also include a step 380 of displaying information.

Note that the above mentioned systems and methods change the magnetic field of the AC generator without measuring the voltage or current generated by the AC generator. It is not necessary to measure the power output by the AC generator or to compare the measured power with a reference power. This simplifies the control design.

While the invention has been described in terms of a limited number of embodiments, it will be understood that many variations, modifications and other applications of the invention may be implemented.

Claims (40)

A system for providing alternating current (AC) voltage, the system comprising: An AC generator for outputting an AC output signal and including a shaft that rotates at a rotational speed followed by an AC rotor; A speed sensor detecting the rotation speed; And A controller for controlling the magnetic field of the AC generator in response to the rotational speed Including, And the controller comprises a direct current (DC) generator for generating a current provided to the AC generator to control the magnetic field of the AC generator. The method of claim 1, And the DC generator comprises a DC rotor following the shaft. The method of claim 2, The DC rotor is coupled with the AC rotor. The method of claim 2, The DC rotor is coupled to the AC rotor by a rigid winding. The method of claim 1, And said DC generator comprises a DC stator supplied by an excitation voltage having an amplitude responsive to said rotational speed. The method of claim 1, And the controller includes a voltage change rate system that receives rotational speed information from the speed sensor and determines an amplitude of an excitation voltage provided to the DC generator. The method of claim 6, And the voltage change rate system determines the amplitude of the excitation voltage in response to the relationship between the peak voltage of the AC output voltage and the rotational speed. The method of claim 6, The voltage rate change system is: An analog to digital converter for converting analog rotational speed information into digital rotational speed information; A low pass filter for filtering the digital rotation speed information to provide filtered rotation speed information; A processor for determining the excitation voltage in response to filtered digital rotation speed information and in response to a relationship between the peak voltage and the rotation speed of an AC output voltage; And And a digital to analog (DA) converter for converting the digital control signal output from the processor into an analog signal for controlling the amplitude of the excitation voltage. The method of claim 1, A rotational speed sensor for generating digital rotational speed information. The method of claim 1, And the controller comprises a voltage change rate system that receives rotational speed information and the requested peak voltage of the AC output signal from the speed sensor and determines the amplitude of the excitation voltage provided to the DC generator. The method of claim 1, And the shaft is rotated by a mechanical pressure element powered by a renewable energy source. The method of claim 1, And said renewable energy is selected from the group consisting of wind, water, sun and geothermal energy. The method of claim 1, And a mechanical input element for rotating said rotor. The method of claim 1, And a cooling fan subsequent to said shaft. The method of claim 1, And the controller controls the magnetic field of the AC generator to keep the peak voltage of the AC output signal substantially constant despite the change in the rotational speed. The method of claim 15, And the DC generator comprises a DC rotor following the shaft. The method of claim 16, The DC rotor is coupled with the AC rotor. The method of claim 15, And said DC generator comprises a DC stator supplied by an excitation voltage having an amplitude responsive to said rotational speed. The method of claim 15, And the controller comprises a voltage change rate system that receives rotational speed information from the speed sensor and determines an amplitude of an excitation voltage supplied to the DC generator. The method of claim 15, And the shaft is rotated by a mechanical input element powered by a renewable energy source. A method of providing an alternating current (AC) voltage, the method comprising: Sensing the rotational speed of the shaft; Controlling a magnetic field of an AC generator in response to the rotational speed, the controlling comprising providing current to the AC generator by a direct current (DC) generator; And Outputting an AC output voltage by the AC generator; Including, The peak voltage of the AC output signal is in response to the magnetic field of the AC generator, And the AC generator comprises an AC rotor following the shaft. The method of claim 21, The controlling step includes providing a current by the DC generator, And said DC generator has a DC rotor following said shaft. The method of claim 22, The DC rotor is coupled with the AC rotor. The method of claim 21, The DC rotor of the DC generator is coupled to the AC rotor by a rigid winding. The method of claim 21, Supplying a DC stator of the DC generator by an excitation voltage having an amplitude responsive to the rotational speed. The method of claim 21, Receiving rotational speed information from a speed sensor and determining an amplitude of an excitation voltage provided to the DC generator. The method of claim 26, In response to the relationship between the peak voltage of the AC output voltage and the rotational speed, determining an amplitude of the excitation voltage. The method of claim 26, Converting analog rotational speed information into digital rotational speed information; Low pass filtering the digital rotation speed information to provide filtered rotation speed information; Determining the excitation voltage in response to filtered digital rotational speed information and in response to a relationship between the peak voltage and the rotational speed of the AC output voltage; Generating a digital control signal responsive to said determining; And Converting the digital control signal into an analog signal for controlling the amplitude of the excitation voltage. The method of claim 28, Providing digital rotational speed information by the rotational speed sensor. The method of claim 28, Receiving rotational speed information and a requested peak voltage of the AC output signal from a speed sensor and determining the amplitude of the excitation voltage provided to the DC generator. The method of claim 21, And the shaft is rotated by a mechanical input element powered by a renewable energy source. The method of claim 21, The renewable energy is selected from the group consisting of wind, water, sun and geothermal energy. The method of claim 21, Rotating the shaft by a mechanical input element. The method of claim 21, Activating a cooling fan subsequent to said shaft. The method of claim 21, Controlling the magnetic field of the AC generator to maintain a substantially constant peak voltage of the AC output signal despite a change in the rotational speed. The method of claim 34, wherein And said DC generator comprises a DC rotor following said shaft. 36. The method of claim 35 wherein The DC rotor is coupled to the AC rotor. The method of claim 34, wherein And the shaft is rotated by a mechanical input element powered by a renewable energy source. The method of claim 34, wherein Supplying a DC stator of the DC generator by an excitation voltage having an amplitude responsive to the rotational speed. The method of claim 34, wherein Receiving rotational speed information from a speed sensor and determining an amplitude of an excitation voltage provided to the DC generator.

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