JP2010523075A - System and method for generating an alternating output signal - Google Patents

Abstract

Systems and devices for providing AC signals. The system outputs an AC output signal and includes an AC generator having an AC rotor coupled to a shaft rotating at a rotational speed, a speed sensor for sensing the rotational speed, and an AC generator according to the rotational speed A controller for controlling the magnetic field of the AC generator, the controller comprising a direct current (DC) generator that generates a current provided to the AC generator to control the magnetic field of the AC generator.
[Selection] Figure 1

Description

[Related applications]
This application claims priority to US Provisional Patent Application No. 60 / 907,248, filed Mar. 27, 2007, which is fully described herein and incorporated by reference.

  The present invention relates to systems and devices for generating electricity with constant output but with the possibility of variable speed, and more particularly to such systems and devices featuring a voltage regulation system.

  The generation of electricity through the use of electric generators is important in current life. These generators require operating several external energy sources, for example, some types of fossil fuel and / or renewable energy. The generator then consumes an energy source to generate electricity. However, it is important that the power output remains constant in order to make the generated electricity useful.

  If the generator shaft speed remains constant, the power output can remain constant. However, the generator shaft speed cannot always be kept constant. Therefore, some generators rely on maintaining at least a minimum speed so that the power output provided is determined by the minimum speed of the shaft. If the shaft speed increases beyond the minimum value, the excess power generated is discarded and thus wasted.

  Various solutions are contemplated, but none completely solve the problem for alternating current (AC) generators. For example, US Pat. No. 5,541,483 provides a method for controlling a direct current (DC) motor or generator, particularly of the permanent magnet type. Due to the functional differences between AC and DC generators, the described solution is not effective for AC generators.

  U.S. Patent Application 2004/0257050 describes a method and device for generating a constant current, which is intended to overcome the disadvantages associated with shaft speed variability through the step of controlling the current output by the generator. To obtain a certain level of output current. Accordingly, the described invention relates to the stabilization of relatively complex currents.

  Various solutions contemplated for obtaining a stabilized voltage output vary using either inertia or friction as a means of mitigating shaft speed fluctuations, or using torque control to control shaft speed, or vary. Converting AC electricity to DC electricity and standard grid AC power. Clearly, all of these methods are very wasteful of energy.

  In an attempt to use renewable energy sources, “natural” energy was used, such as wind power through the use of wind turbines, solar power through the use of solar panels, hydropower such as wave or tide forces, etc. Systems and devices are introduced. Wind energy is particularly variable considering that wind power increases and decreases momentarily and / or changes direction. However, all “natural” energy sources are expected to experience power level instability. Therefore, the ability to convert unstable mechanical power to stable power for renewable energy is a major demand in a variety of applications.

  Various solutions have been proposed in the field to overcome the instability of renewable energy sources, particularly for wind generation. For example, US Pat. No. 7,068,015 provides a wind solution by adjusting the magnetic field according to the rotational speed of the wind turbine according to feedback determined by measuring the output voltage or current. U.S. Patent Application 2004/0119292 provides a method for controlling the shaft speed of a generator by controlling the torque, i.e. a solution to the above weaknesses. The taught method further requires a diode rectifier for operation, which is another weakness.

  U.S. Pat. No. 5,083,039 controls the power output by controlling the generator magnetic field, i.e. by controlling the stator current. However, changes in stator current cause changes in generator torque. To compensate for torque changes, shaft speed is controlled by changing turbine “wings” or blade gradients, which can be a weak point depending on wind conditions, and further energy consumption. Is a weak point in any case. U.S. Pat. No. 6,137,187 has the same weaknesses as requiring a gradient control system.

  The term “constant electrical output” means an AC 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 AC generator magnetic field in response to the sensed speed. The control step includes using a DC generator that supplies current to the AC generator. This current determines the magnetic field of the AC generator. The magnetic field can be controlled in a manner that maintains the peak voltage of the output signal of the AC generator substantially constant regardless of changes in the rotational speed of the shaft.

  The electromagnetic force induced by the AC generator is determined by the following Faraday law.

は巻線の接線速度である。 Here, EMF (electromagnetic field) is an output voltage,

Is the tangential speed of the winding.

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

  B is the magnetic field strength.

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

  The above equation shows that the peak voltage of the AC output signal of the AC generator depends on the rotational speed of the shaft and also on the mechanical force used to rotate the shaft. If the mechanical force level is variable, then the rotational speed of the shaft is also variable. However, the peak voltage should be kept substantially constant even if the rotational speed of the shaft is variable.

  Thus, the present invention does not require constant shaft rotation speed, and includes, but is not limited to, power generation by renewable energy, or “natural” energy sources, or energy sources with other variable outputs. Useful for various applications. Instead, according to an aspect of the present invention, the measurement of shaft rotational speed is used to control the magnetic field strength (B) through feedback or control mechanisms (including DC generators) according to the rotational speed of the shaft, thereby Provides constant voltage output and thus stable power generation.

  According to an aspect of the present invention, control of the magnetic field strength of an AC generator is preferably provided with a DC generator and features a rotor winding coupled to the rotor winding of the AC generator. The rotation speed of the AC generator shaft is measured, and this measurement allows the operation of the DC generator to be used to increase or decrease the magnetic field strength, thereby producing a constant voltage output even if the rotation speed of the shaft changes. maintain. The DC generator optionally and preferably has a separate power source. Preferably, the amount of power required for management and control of the voltage output is relatively low compared to the output of the generator itself, for example, the tests described below show that the required control power is 30 W for a 5 kW generator. Less than. Optionally and preferably, the rotor winding of the DC generator is coupled to the rotor winding of the AC generator for controlling the magnetic field of the AC generator.

  A system for providing an alternating current (AC) voltage, wherein the system outputs an AC output signal and includes an AC generator coupled to a shaft that rotates at a rotational speed, and senses the rotational speed. And a controller for controlling the magnetic field of the AC generator according to the rotational speed, the controller generates a current provided to the AC generator to control the magnetic field of the AC generator A direct current (DC) generator.

  Conveniently, the DC generator comprises a DC rotor that is coupled to the shaft.

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

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

  Conveniently, the DC generator comprises a DC stator when powered by an excitation voltage having an amplitude depending on the rotational speed.

  Conveniently, the controller comprises 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 regulation system determines the amplitude of the excitation voltage as a function of the relationship between the rotational speed and the peak voltage of the AC output voltage.

  Conveniently, the voltage regulation system filters the digital rotational speed information to provide an AD converter that converts the analog rotational speed information into digital rotational speed information and the filtered rotational speed information. A low-pass filter, a processor for determining the excitation voltage according to the filtered digital rotational speed information, and the relationship between the rotational speed and the peak voltage of the AC output voltage, and the digital output from the processor A DA converter for converting the control signal into an analog signal for controlling the amplitude of the excitation voltage;

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

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

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

  Conveniently, the renewable energy is selected from the group consisting of wind power, hydraulic power, solar heat, and geothermal heat.

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

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

  Conveniently, the controller controls the magnetic field of the AC generator to maintain the AC output peak voltage substantially constant regardless of changes in 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 present invention is described herein for purposes of illustration with reference to the accompanying figures. With particular reference to the detailed drawings, the features shown are for illustrative purposes only and for purposes of exemplary discussion of aspects of the invention and are considered to be most useful as those of the invention. Claims are provided to provide an easily understood description of the principles and conceptual aspects. In this respect, no attempt is made to show the details of the structure of the present invention in more detail than is necessary for a basic understanding of the present invention, and the description using the figures shows how It will be clear to those skilled in the art whether this form is actually embodied.

FIG. 1 is an AC generator system exemplarily shown according to the present invention. FIG. 2 is a method illustratively shown by the present invention for controlling the operation of the generator of FIG. FIG. 3 is a more detailed but schematic diagram of a voltage regulation system according to the present invention. FIG. 4 is a schematic block diagram of an exemplary system according to the present invention for the generation of a constant level voltage by a generator that is at least partially powered by a renewable energy source or “natural” energy. FIG. 5 shows the test results of an exemplary system according to the present invention. FIG. 6 illustrates a voltage regulation system and rotational speed sensor in more detail according to an aspect of the present invention. FIG. 7 illustrates a voltage regulation system and rotational speed sensor in more detail according to an aspect of the present invention. FIG. 8 illustrates a voltage regulation system and rotational speed sensor in greater detail according to an aspect of the present invention. FIG. 9 shows the relationship between control current and shaft rotation speed for different values of the peak voltage of the AC output signal. FIG. 10 shows the relationship between control current and shaft rotation speed for different values of the peak voltage of the AC output signal. FIG. 11 illustrates a method according to an aspect of the present invention.

  The present invention is a system and device for providing constant voltage power (meaning an AC output signal having a substantially constant peak voltage) by an AC generator through control of the magnetic field strength of the AC generator. A DC generator is used. The magnetic field strength is controlled by the current supplied by the DC generator and by the rotational speed of the AC generator shaft so that changes in the rotational speed of the shaft are compensated by changes in the magnetic field strength.

  According to an aspect of the present invention, a DC generator featuring a rotor winding is electrically connected to a rotor winding of an AC generator. The rotational speed of the shaft of the AC generator is preferably measured, and this measurement allows the operation of the DC generator to be used to increase or decrease the magnetic field strength so that even if the rotational speed of the shaft changes, the constant voltage Maintain output.

  Optionally and preferably, the rotor winding of the DC generator is coupled to the rotor winding of the AC generator for controlling the magnetic field of the AC generator.

  The present invention may optionally be used with any mechanical force source, but is useful for any mechanical force input source 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, hydraulic, solar or geothermal.

  In accordance with an optional aspect of the present invention, in addition to providing a constant voltage output, the AC generator magnetic field is selectively controlled by a number of criteria, such as setpoints. The setpoint may optionally be within a minimum required setpoint or maximum allowable setpoint for the voltage output and / or within an allowable setpoint.

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

  According to the figure, FIG. 1 is an illustratively illustrated AC generator system 100 for generating a constant level of output voltage. The generator system 100 features a connection to mechanical force from a power source (not shown) and causes the shaft 106 of the AC generator 108 to rotate. The shaft 106 further optionally features a cooling fan 104 for cooling the operation of the generator system 100. The AC generator 108 is preferably a three-phase double winding generator and features a rotor 110 and a stator 112. The rotor 110 preferably features a rotor winding 114 and the stator 112 preferably features a stator winding 116.

  An auxiliary DC generator 118 is optionally and preferably installed on the shaft 106 as shown to control the magnetic field strength of the AC generator 108. The DC generator 118 features a DC rotor 120 having a DC rotor winding 122 and a DC stator 124 having a DC stator winding 126. The DC rotor winding 122 is preferably coupled to the rotor winding 114 of the AC generator 108 through a connector 130 and preferably comprises several types of wiring, optionally with the DC rotor winding 122 being a rotor winding. A fixed wiring may be used so as to rotate at the same speed as the line 114. The DC stator winding 126 is coupled to a DC power supply 128 through a suitable connector 132 as is known in the art.

  A rotational speed sensor (also referred to as a speed sensor) 134 is preferably coupled to the shaft 106 to sense the rotational speed of the shaft 106. The rotational speed sensor 134 may optionally feature any suitable speed sensing device, including, but not limited to, a shaft encoder, resolver, tachometer, Hall effect sensor, or any optional reading of feature points on the outer periphery of the shaft 106. Including proximity sensors of the type. The feature points include any type of feature, including but not limited to notches, screws, or holes.

  The voltage regulation system 136 is electrically coupled to the rotational speed sensor 134 and the DC power supply 128. Any type of programmable or computer device, or digital circuit, or any device featuring software, firmware or hardware, or a combination thereof may be used selectively, but the voltage regulation system 136 is preferred. Is based on PLC (programmable logic controller).

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

  The rotational speed sensor 134 senses the rotational speed of the shaft 106. This information is supplied to a voltage regulation system 136 that controls the DC power supply 128 to change the excitation voltage in the DC stator 124, thereby changing the EMF output by the DC generator 118. In addition, it controls the magnetic field strength of the AC generator 108 by changing the current in the rotor winding 114.

  The excitation voltage is selectively and preferably determined by a voltage regulation system 136 according to the method shown in FIG. FIG. 2 is a method illustratively shown by the present invention for controlling the operation of the generator of FIG. As shown, in stage 1, the actual rotational speed (also referred to as shaft speed) of the AC generator shaft is measured by a rotational speed sensor. In stage 2, the voltage regulation system changes the value of the DC power supply control input, preferably changing the excitation voltage of the DC stator. Optionally and preferably both steps are repeated as necessary, but step 1 is repeated at least once.

  Preferably, the output voltage is first measured in relation to the rotational speed to define a control voltage curve for a particular generator. Once this curve is built for the generator, it is used to perform the above method.

  The method may optionally be further used to change the “set point” of the output signal of the AC generator. For example, such a method can be used to selectively increase or decrease the peak voltage of the output signal supplied by the AC generator. Optionally, increasing or decreasing the peak voltage of the output signal can be useful in a variety of situations, such as when the level of mechanical force input to the AC generator changes. As described in greater detail below, such input mechanical force changes may occur for any type of energy source, but may regenerate like wind or other types of “natural” energy sources. It is especially generalized about possible energy sources. Preferably, increasing or decreasing the level of the output voltage in this way is done for a mechanical force input source characterized by variability.

  FIG. 3 is a more detailed but schematic diagram of a voltage regulation system according to the present invention. In stage 1, as described above, the control voltage curve is determined for each generator system, preferably during system formation. This stage is not necessarily repeated once the system is operational.

  Steps 2-5 are preferably repeated at least once, more preferably as a loop, continuously as needed. In stage 2, the AC generator is in operation and the AC generator shaft is rotating. In stage 3, the rotational speed of the shaft is measured by a rotational speed sensor as described in FIG. In step 4, the amount of control voltage to be output is determined using the rotational speed of the shaft and the control voltage curve. In stage 5, a control voltage is output by a control voltage output generator, which is preferably an associated DC generator as described in FIG.

  FIG. 4 is a schematic block diagram of an exemplary system according to the present invention for the generation of a constant level voltage by a generator that is at least partially powered by a renewable energy source or “natural” energy. As shown, the system 400 features a mechanical power source 402 and optionally and preferably several types of renewable energy selected from the group consisting of wind, solar, hydro, and geothermal. A device powered by source or “natural” energy. The system 400 further preferably features an AC generator system 404 and can be implemented, for example, as described with respect to FIGS. 1 and / or 2 and / or 3.

  Mechanical force source 402 is mechanically coupled to shaft 406 of AC generator 408 that is part of AC generator system 404, thereby rotating shaft 406. The mechanical force source 402 is a selectively and preferably variable power source in the sense that the mechanical force output level can be variably operative. Such fluctuation causes fluctuation in the rotation speed of the shaft 406. However, the voltage regulation system 410 of the AC generator system 404 is such that the AC generator system 404 provides an AC output signal having a peak voltage that is maintained at a constant level regardless of any variation in the rotational speed of the shaft 406. To control the magnetic field in the AC generator 408.

  Among the many advantages of the exemplary embodiment of the present invention shown in FIG. 4, the provision of a constant AC output signal peak voltage is that of wind, hydro (hydropower), solar, geothermal or other types of turbines. This can be done without changing or affecting the structure or function. Thus, the function and design of the turbine itself is selected for obtaining the most effective energy from renewable energy sources. Background art citations do not teach or suggest a system or device for generating a constant level output voltage from a renewable energy source.

[Examination system test]
This example describes tests performed on the non-limiting system illustrated in the examples by the present invention. The system featured a hybrid double-winding three-phase generator known in the art. It includes both DC and AC generators with product number ECO3-2S4 (MecCalte SpA, Italy) and a programmable logic controller (PLC) with CQM-45 (Omron, USA). Yeah. The system setpoint voltage was 285 Vac. The AC generator was powered by an electric motor connected to a variable speed motor driver. The rotational speed of the AC generator shaft was then changed according to the speed of the motor. For each rotational speed, the excitation voltage of the auxiliary DC generator was changed until the peak voltage of the AC output reached the setpoint value (285 Vac).

  FIG. 5 shows the auxiliary excitation voltage value of the DC generator according to the shaft speed of the AC generator when required to maintain a constant voltage output by the AC generator.

  FIG. 6 illustrates the voltage regulation system 136 and the rotational speed sensor 134 in greater detail according to an aspect of the present invention.

  The rotation speed sensor 134 provides the analog rotation speed information to the AD converter 161 that converts the analog rotation speed information into digital rotation 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. Although the low-pass filter 162 can apply fast Fourier transform filtering processing, it is not always necessary to do so.

  A processor 164, such as an FPGA, determines the excitation voltage depending on the filtered digital rotational speed information and the relationship between the rotational speed and the peak voltage of the AC output voltage. Information representing this relationship can be stored in the FPGA, and instructions executed by the FPGA can be stored in a memory unit such as EPROM 165.

  The processor 164 outputs a digital control signal representing the decision to the 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 provided to a DC power supply 128 and supplied to a current driver 168 that provides a current signal that determines the excitation voltage output by the power supply 128. The signal or analog control signal output by current driver 168 can be measured by voltmeter 171 and displayed on the display of the voltmeter. A multiplexer 169 or other sampling circuit may be provided between the current driver 168 and the output port of the voltage regulation system 136 to allow such measurements and provision of current signals to the DC power supply 128.

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

  A protocol converter 163 or another port or interface may be used to provide the required peak voltage to the voltage regulation system 136.

  Ports or interfaces (or additional ports or interfaces) can be used to provide web-based management as illustrated by FIG. The web-based management entity 175 of the voltage regulation system 136 allows measurement of rotational speed measurement data and / or analog signals output to the DC power supply 128 and is output to one or more external devices and / or , Allowing one or more user interactions with the voltage regulation system 136. The web-based management entity 175 can be software, firmware, hardware, or a combination thereof.

  Returning to FIG. 6, the voltage regulation system 136 can be attached to a printed circuit board. Additionally or alternatively, it can communicate with a web server (not shown) that can provide one or more web pages. These web pages serve as interfaces for voltage regulation systems 136 for users, eg, simple configuration options, as is known in the art.

  The voltage regulation system 136 can output information to a display, such as a rotational speed display 172, as well as a display of the voltmeter 171 or a combination thereof. Information can be provided via a port or interface.

  According to another aspect of the invention, the rotational speed sensor provides digital rotational speed information and does not provide analog rotational speed information. FIG. 7 illustrates a rotational speed sensor that includes an incremental encoder 134 '. Incremental encoder 134 'generates digital rotational speed information, and thus does not require voltage regulation system 136 of various configurations (such as AD converter 161 and digital low pass filter 162).

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

  A number of curves represent the relationship between control current and shaft rotation speed for different peak voltages of the AC output signal.

  FIG. 11 illustrates a method 300 according to an aspect of the present invention.

  Method 300 begins at step 310 or step 320.

  Stage 310 includes determining a required peak voltage of the AC output signal output by the AC generator.

  Stage 320 includes receiving information representative 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 sensing the rotational speed of the shaft.

  The method 300 may comprise rotating the shaft with a mechanical input element. This stage is not shown for simplicity of explanation. The shaft can be rotated by a mechanical input element powered by a renewable energy source. The renewable energy can be wind, hydraulic, solar and geothermal energy sources.

  Step 330 is followed by step 340 of controlling the AC generator magnetic field as a function of rotational speed.

According to various aspects of the invention, step 340 comprises at least one of the following steps or combinations thereof:
(I) determining 342 the amplitude of the excitation voltage provided to the DC stator of the DC generator as a function of the relationship between the rotational speed and the peak voltage of the AC output voltage. The DC generator can have a DC rotor coupled to the shaft. The DC rotor can be connected to the AC rotor, for example, by fixed wiring. The amplitude can be determined so as to maintain the peak voltage of the AC output signal substantially constant regardless of the change in the rotational speed.
(Ii) Stage 344 of supplying power to the DC stator of the DC generator by the excitation voltage, and the excitation voltage has an amplitude corresponding to the rotational speed.
(I) Stage 346 of providing a control current to the AC generator by a direct current (DC) generator, the control current depending on 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 depends on the magnetic field of the AC generator. The AC generator includes an AC rotor that is coupled to the shaft.

  The decision stage 342 may comprise at least one of the following stages or combinations thereof: (i) receiving rotational speed information from a speed sensor 342 (1), (ii) requesting an AC output voltage Receiving a peak voltage 342 (2), determining an excitation voltage amplitude 342 (3) as a function of the relationship between the control current and the shaft rotational speed, (iv) the control current value, the shaft rotational speed, and Determining the amplitude of the excitation voltage as a function of the relationship between the requested peak voltages of the AC output voltage 342 (4);

  Note that changing the required peak voltage of the AC output signal changes the “setpoint” of the system. As the peak voltage changes, the relevant curve (or equation) should be selected by decision. Accordingly, stage 344 may include selecting between curves as shown in FIG.

  According to an aspect of the invention, the determination is performed in the digital domain. Accordingly, stage 344 includes (i) converting analog rotational speed information to digital rotational speed information, and (ii) applying a low pass filter to the digital rotational speed information to provide filtered rotational speed information. Determining the excitation voltage according to the step, (iii) the filtered digital rotational speed information, and the relationship between the rotational speed and the peak voltage of the AC output voltage, and (iv) the digital according to the determination. Generating a control signal; and (v) converting the digital control signal into an analog signal that controls the amplitude of the excitation voltage.

  Method 300 may further include actuating 370 a cooling fan coupled to the shaft. The cooling fan is operated by a shaft. The method 300 may further include displaying 380 information.

  It should be noted that the systems and methods described above change the AC generator's magnetic field without measuring the current or voltage generated by the AC generator. There is no need to approximate the power output by the AC generator or to compare the approximate power with a reference power. This simplifies the control scheme.

  Although the invention has been described in a limited number of ways, it will be apparent that many variations, modifications and other applications of the invention may be made.

Claims (40)

A system for providing an alternating current (AC) voltage, the system comprising:
An AC generator that outputs an AC output signal and includes an AC rotor coupled to a shaft that rotates at a rotational speed;
A speed sensor for sensing the rotational speed;
A controller for controlling the magnetic field of the AC generator according to the rotational speed;
And wherein the controller comprises a direct current (DC) generator that generates a current provided to the AC generator to control the magnetic field of the AC generator.   The system of claim 1, wherein the DC generator comprises a DC rotor that is coupled to the shaft.   The system of claim 2, wherein the DC rotor is coupled to the AC rotor.   The system according to claim 2, wherein the DC rotor is connected to the AC rotor by a fixed wiring.   The system according to claim 1, further comprising a DC stator when the DC generator is supplied with an excitation voltage having an amplitude corresponding to the rotational speed.   The system of claim 1, wherein the controller comprises a voltage regulation system that receives rotational speed information from the speed sensor and determines an amplitude of an excitation voltage provided to the DC generator.   7. The system of claim 6, wherein the voltage regulation system determines an amplitude of the excitation voltage according to a relationship between the rotational speed and a peak voltage of the AC output voltage. 7. The system of claim 6, wherein the voltage regulation system is
An AD converter that converts analog rotational speed information into digital rotational speed information;
A low pass filter for filtering the digital rotational speed information to provide filtered rotational speed information;
A processor for determining the excitation voltage according to the filtered digital rotational speed information and the relationship between the rotational speed and the peak voltage of the AC output voltage;
A DA converter for converting the digital control signal output from the processor into an analog signal for controlling the amplitude of the excitation voltage;
A system characterized by comprising.   9. The system of claim 8, comprising a rotational speed sensor that has generated digital rotational speed information.   The system of claim 1, wherein the controller receives rotational speed information from the speed sensor and a requested peak voltage of the AC output signal to determine an amplitude of an excitation voltage provided to the DC generator. A system characterized by comprising a voltage regulating system.   The system of claim 1, wherein the shaft is rotated by a mechanical input element powered by a renewable energy source.   The system of claim 1, wherein the renewable energy is selected from the group consisting of wind power, hydraulic power, solar heat, and geothermal heat.   The system of claim 1, further comprising a mechanical input element for rotating the rotor.   The system of claim 1, further comprising a cooling fan coupled to the shaft.   The system of claim 1, wherein the controller controls the magnetic field of the AC generator to maintain a substantially constant peak voltage of the AC output signal regardless of changes in the rotational speed. Feature system.   16. The system according to claim 15, wherein the DC generator comprises a DC rotor that is coupled to the shaft.   The system of claim 16, wherein the DC rotor is coupled to the AC rotor.   16. The system according to claim 15, further comprising a DC stator when the DC generator is powered by an excitation voltage having an amplitude corresponding to the rotational speed.   16. The system of claim 15, wherein the controller comprises a voltage regulation system that receives rotational speed information from the speed sensor and determines an amplitude of an excitation voltage provided to the DC generator.   16. The system of claim 15, wherein the shaft is rotated by a mechanical input element that is powered by a renewable energy source. A method for supplying an alternating current (AC) voltage, the method comprising:
Sensing the rotational speed of the shaft;
A step of controlling the magnetic field of the AC generator in response to the rotational speed, the step comprising providing a current from a direct current (DC) generator to the AC generator;
Outputting an AC output voltage by the AC generator;
And the AC generator comprises an AC rotor coupled to the shaft in response to a peak voltage of the AC output signal depending on the magnetic field of the AC generator.   23. The method of claim 21, wherein the controlling step comprises providing the current by the DC generator, the DC generator having a DC rotor coupled to the shaft.   23. The method of claim 22, wherein the DC rotor is coupled to the AC rotor.   The method of claim 21, wherein the DC rotor of the DC generator is coupled to the AC rotor by a fixed wire.   The method according to claim 21, comprising feeding a DC stator of the DC generator with an excitation voltage having an amplitude corresponding to the rotational speed.   The method of claim 21 comprising receiving rotational speed information from the speed sensor and determining an amplitude of an excitation voltage provided to the DC generator.   27. The method of claim 26, comprising determining an amplitude of the excitation voltage as a function of a relationship between the rotational speed and a peak voltage of the AC output voltage. The method of claim 26, wherein:
Converting analog rotational speed information into digital rotational speed information;
Applying a low pass filter to the digital rotational speed information to provide filtered rotational speed information;
Determining the excitation voltage according to the filtered digital rotational speed information and the relationship between the rotational speed and the peak voltage of the AC output voltage;
Generating a digital control signal in response to the determination;
Converting the digital control signal into an analog signal for controlling the amplitude of the excitation voltage;
A method characterized by comprising.   30. The method of claim 28, comprising providing digital rotational speed information by a rotational speed sensor.   30. The method of claim 28, receiving rotational speed information from the speed sensor and a requested peak voltage of the AC output signal, and determining an amplitude of an excitation voltage provided to the DC generator. And a step.   The method of claim 21, wherein the shaft is rotated by a mechanical input element powered by a renewable energy source.   23. The method of claim 21, wherein the renewable energy is selected from the group consisting of wind power, hydraulic power, solar heat, and geothermal heat.   The method of claim 21, comprising rotating the shaft by a mechanical input element.   23. The method of claim 21, comprising activating a cooling fan that is coupled to the shaft.   22. The method of claim 21, comprising controlling the magnetic field of the AC generator to maintain a peak voltage of the AC output signal substantially constant regardless of the change in rotational speed. A method characterized by.   35. The method of claim 34, wherein the DC generator comprises a DC rotor that is coupled to the shaft.   36. The method of claim 35, wherein a DC rotor is coupled to the AC rotor.   35. The method of claim 34, wherein the shaft is rotated by a mechanical input element powered by a renewable energy source.   35. The method of claim 34, comprising feeding the DC stator of the DC generator with an excitation voltage having an amplitude that depends on the rotational speed.   35. The method of claim 34, comprising receiving rotational speed information from the speed sensor and determining an amplitude of an excitation voltage provided to the DC generator.

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