Classifications

• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
  • H02P9/14—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field
  • H02P9/26—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices
  • H02P9/30—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices using semiconductor devices
  • H02P9/305—Arrangements for controlling electric generators for the purpose of obtaining a desired output by variation of field using discharge tubes or semiconductor devices using semiconductor devices controlling voltage
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K16/00—Machines with more than one rotor or stator
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02K—DYNAMO-ELECTRIC MACHINES
  • H02K19/00—Synchronous motors or generators
  • H02K19/16—Synchronous generators
  • H02K19/26—Synchronous generators characterised by the arrangement of exciting windings
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P9/00—Arrangements for controlling electric generators for the purpose of obtaining a desired output
  • H02P9/007—Control circuits for doubly fed generators
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
  • H02P2101/00—Special adaptation of control arrangements for generators
  • H02P2101/15—Special adaptation of control arrangements for generators for wind-driven turbines

Definitions

• the present invention relates in general to a method and an apparatus, of converting mechanical torque in constant frequency electricity regardless the rotating speed. It more particular relates to such a method and apparatus useful in providing constant frequency electricity to a utility grid.
• This methods and apparatus can be used in any electrical power production field such as wind generators, gas and hydraulic turbines, Stirling engines, etc.
• BACKGROUND ART Various different techniques have been employed in converting mechanical torque to constant frequency electricity for supplying it to a utility grid.
• stator coils induced voltages are sinusoidal with a magnitude that depends on the rotor DC current, differ by 120° in time and have a frequency determined by the rotating speed of the rotor and its number of poles (e.g. for a rotor with a pair of poles and rotating at 3000 rounds per minute the induced Stator voltage frequency is 50 Hz). For that reason the synchronous generators need to rotate at constant speed in order to produce a AC Voltage at constant frequency.
• the synchronous generator includes a device to control the rotor DC current for the AC electricity produced by the stator to be in phase with the utility grid voltage without any substantial phase shift and maintains the power factor above a mkdmum limit.
• a method and apparatus for converting mechanical torque generated electricity to constant frequency electricity for supplying it to a utility grid regardless the rotating speed of the apparatus.
• the disclosed method and apparatus use two stators and two rotors and a control unit providing two distinct excitation currents for the two rotors. These currents are not necessarily constant in time but they may oscillate with the same frequency and magnitude, but different phases. Assuming the two rotors poles have the same orientation and same winding shape, then the coils of the two stators are wound with a different angle with respect each others. This looks like two synchronous generators coupled (the two rotors have the same rotating speed and possibly they are on the same shaft).
• each of the stator coils produces a voltage without any specific frequency, but the sum of the stators' voltages is a perfect wave, its frequency is equal to the sum of the rotor coils rotating speed and excitation currents frequency.
• the control unit collects data from the sensors like the tachometer for rotor spin and position, the total voltage meter and 1he total current meter produced by the generator.
• the current meter and the voltage meter monitors the current, the power produced by the generator and its power factor.
• the desired power factor of the AC electricity from the stators is achieved by rotors' currents control.
• a calculation of desired rotors' currents magnitude is then performed by the control unit. In case the power factors has decreased the above mentioned device increases excitation currents magnitude in order to keep the power factors above a minimum limit.
• the tachometer monitors the shaft speed and position of the rotors and a calculation of desired rotors' currents frequency is then performed by the control unit in order to maintain the generated power at the desired frequency (e.g. 50 Hz for EU country , 60 for US) within a narrow tolerance.
• the calculation for currents' phases difference is performed keeping the phases difference at a predicted value.
• the above mentioned control unit increases the excitation currents frequency.
• These calculations may also include using closed loop controllers such as proportional , integral and derivative controllers.
• the control unit generates two low power voltage analog outputs proportional to the two rotors currents. These are then amplified by operational amplifiers in order to obtain the proper currents magnitudes for the two rotors.
• the control unit can also takes care of disturbances like residual magnetism of the rotors or the mutual inductance differences. These effects may be included in the rotors currents calculation in the sense that the rotors currents can have bias to nullify tibe residual magnetism of the rotors or the excitation current can have different magnitudes in case the two generators have slightly different mutual inductance.
• FIG. 1 a shows Generator “A”, composed by rotor “A” and stator “A” (respectively ROT A and STAT-A), where ⁇ is the time dependant position of the rotor “A” with respect to the Stator “A”, schematically represented by a single loop.
• - Figure Ib shows the trend of the rotor "A” excitation current (I_a)
• FIG. 2a shows generator "B” , composed by rotor “B” and stator “B” (respectively ROTJB, and STATJB), where ⁇ is the time dependant position of the rotor “B” with respect to the stator "B”, schematically represented by a single loop.
• FIG. 2c shows the trend of the induced voltage in the coil of the Stator "B" (V_b ).
• - Figure 3 shows how the two stators coils are connected each, other and the Trend for total induced voltage V_ab (sum of the two voltage : V_a +V_b ).
• FIG. 4 shows a symbolic block diagram for the generator and its control Unit (CJLJ) and how it is connected to Utility grid. Ih the figure are shown also the two rotors' currents operational amplifiers, (respectively AMP_A and AMPJB), the rotors' position and spin meter (m_w_2), the stators coils current meter (m_I_ab) and the stators coils Voltage meter (m__V_ab).
• BESTMODE FOR CARRYING OUT THE INVENTION With first reference to figure 3, the above described electrical generator can be made by coupling two twin synchronous electric generators and including a control unit controlling the two excitation rotors currents. The two generators are twin in the sense their rotors have the same number of poles and same numbers of coils and impedance and their stators have the same number of winding with the same impedance.
• the control unit collects signals from meters such as the Rotors spin meter (m_w_2), the current meter (m_I_ab) of the stators* coils the stators' coils voltage meter (m_V_ab).
• the two rotors excitation currents are tuned by the control unit controlling their frequencies, magnitudes and their phases.
• the currents' phases differ by a quarter of current period.
• control unit C_U
• the performance of the whole system is provided by the control unit (C_U) in order to match the requirements for any synchronous generator connected to utility grid such as power factor, fixed voltage frequency, voltage peak to peak value and produced Voltage to be in phase with utility grid voltage.
• the two rotors Rot_A 9 and RotJB
• Electromagnetic induction is the working principle of the synchronous electric generator.
• One fixed coil on the stator form a closed path placed in a region in which a magnetic field varies with time.
• V an electromagnetic force (V) on this stator coil is generated and it depends on the rate of change of the magnetic flux.
• the time dependent magnetic flux can be provided either by a rotating permanent magnet or by a rotor fed by a constant current (synchronous generator ) rotating inside the stator coil .
• the induced voltage (V) is :
• the electromagnetic forces (V_a and V_b) induced on the fixed coils are function of the first time derivate of the magnetic fluxes :
• V_ab The total electromagnetic force (V_ab) of a couple of synchronous geaerators with rotors fed by two different currents appropriately controlled is a perfect wave and its frequency is the sum of the rotors currents frequency (w_l) and the rotor spin ( w_2). Details about the electrical connections with the two rotors are not considered relevant to the disclosure of the present invention, in case the electrical connections to the two rotors are be provided by brushes, then Control Unit (C_U) and its operational amplifiers are external to the synchronous generators.
• C_U Control Unit
• the operational amplifiers can be installed on the rotors shaft and they can be powered by a permanent magnet generator with diode bridge, in this case the control unit may communicate and drive these amplifiers with, an optical interface.
• the utility grid breaker controls and actuation are not considered relevant to the disclosure of the present invention, these controls are normally made by standard unit in order to prevent spurious AC generated electricity flowing to utility grid. Details about the generator alignment, before utility grid breaker is closed, for the current regulation of the AC electricity produced to be in phase with the utility grid voltage without any substantial phase shift are not considered relevant to the disclosure of the present invention.
• wind turbines coupled to synchronous generator need wind speed above a minimum limit to allow the generator to rotate at constant speed in order to be connected to the electrical grid network, in case of high wind speed regime, the wind generator need to rotate always at the same spin, reducing the overall efficiency.
• Other wind turbines are coupled to permanent magnet generators, they operate at different spin based on the wind load but the produced voltage is first converted to a DC voltage, then an other device, called DC / AC INVERTER to convert the DC voltage into AC voltage for local usage or for the connection to external electrical grid.
• the electric generator described herein coupled to a wind turbine can overcome all these aspects. It can operate at different wind speeds producing directly an AC voltage with a constant frequency (even at lower wind speeds ) and be connected to external power grid without any further conversion of its power (DC/AC Inverter ).

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Eletrric Generators (AREA)

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Publications (1)

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Family Applications (1)

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Cited By (2)

Citations (2)

• 2006
  • 2006-07-26 IT ITNO20060008 patent/ITNO20060008A1/it unknown
• 2007
  • 2007-07-11 WO PCT/IT2007/000492 patent/WO2008012853A1/en not_active Ceased

Patent Citations (2)

Non-Patent Citations (1)

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