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
  • H02P9/48—Arrangements for obtaining a constant output value at varying speed of the generator, e.g. on vehicle
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
  • H02J3/12—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load
  • H02J3/14—Circuit arrangements for ac mains or ac distribution networks for adjusting voltage in ac networks by changing a characteristic of the network load by switching loads on to, or off from, network, e.g. progressively balanced loading
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J2310/00—The network for supplying or distributing electric power characterised by its spatial reach or by the load
  • H02J2310/50—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads
  • H02J2310/56—The network for supplying or distributing electric power characterised by its spatial reach or by the load for selectively controlling the operation of the loads characterised by the condition upon which the selective controlling is based
  • H02J2310/58—The condition being electrical
• • 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
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
  • Y02B70/30—Systems integrating technologies related to power network operation and communication or information technologies for improving the carbon footprint of the management of residential or tertiary loads, i.e. smart grids as climate change mitigation technology in the buildings sector, including also the last stages of power distribution and the control, monitoring or operating management systems at local level
  • Y02B70/3225—Demand response systems, e.g. load shedding, peak shaving
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/70—Wind energy
  • Y02E10/72—Wind turbines with rotation axis in wind direction
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
  • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
  • Y04S20/00—Management or operation of end-user stationary applications or the last stages of power distribution; Controlling, monitoring or operating thereof
  • Y04S20/20—End-user application control systems
  • Y04S20/222—Demand response systems, e.g. load shedding, peak shaving

Definitions

• the invention comprises a technique for limiting the grid-connection current and surplus output of a wind turbine or a similar electricity-generating system for the utilization of renewable energy, and this technique is more specifically of a nature as described in the preface to Claim 1.
• the invention also comprises an electronically controllable power diverter (electrical brake load) for use in this technique.
• an induction motor When an induction motor is driven above synchronous speed, it functions as an electrical generator which converts the added mechanical power of the axle into electric power. If the motor - now an induction generator - is coupled with an alternating-current grid, the current generated will be accepted by the grid. This effect is employed, for example, in modern wind 15 turbines and similar energy systems used to utilize renewable energy sources. It should be noted, however, that the induction motors used in generators are specially developed for this purpose.
• connection takes place at a point when the turbine is running almost load-free, often while the wind is on the rise.
• the windspeed could then be made to rise slowly until the exact point where the turbine rotor rotates at synchronous speed.
• the generator could be coupled to the grid through a relay or some similar, simple electric switch mechanism without causing power surges in the grid or torque discontinuities in the wind power system. In practice, of course, this method is impossible, since windspeed is not a controllable factor.
• MITA TEKNIK A/S has developed an electronically controllable electrical connector which satisfies the need for a fully controllable coupling process. Please see the description in DK Patent Application No.0758/97.
• the grid frequency and voltage will control the generator and thus the turbine itself. In practice, this means that the speed of the turbine motor is determined by the grid frequency. Since the power generated by the turbine depends on the speed of the wind, it is clear that the electric power delivered to the grid varies constantly. Wind power systems are designed to develop a certain nominal yield (rated capacity) at a certain windspeed which from now on will be referred to as the nominal windspeed. For reasons of economy, the grid is usually designed for the same electric power output (i.e. rated capacity). Windspeeds above the nominal - more specifically, in the interval between the nominal windspeed and the windmill's cut-out windspeed - will result in a higher output of electricity from the generator than the grid is designed to accept.
• stall controlling Two different methods are used in the attempt to control the power generated by wind turbines.
• One method is called "stall controlling", and it utilizes the tendency of the blades to stall (lose their lift) when the angle of attack of the blade relative to the airflow exceeds a certain threshold value which is determined by the shape of the blade, and fixed-pitch rotor blades with specially developed aerodynamic blade shapes are used.
• This method of control is not very precise, and it requires oversized gears and generators so the braking torque of the generator on the turbine rotor is sufficient to provoke blade stall at the set windspeed. Just before the blades stall, there is often an undesirable (and uncontrollable) surge in power. In cases where requirements to power quality are high, this control method is inadequate. 3
• the second method is using variable-pitch blades.
• the system required is technically demanding, and in practice it is impossible to vary the pitch of the blades fast enough to match changes in windspeed.
• the result is an undesirable periodical overload of the grid and intermittent periods of power loss because the blades are unable to follow the changes in windspeed adequately, and they thus periodically adopt a pitch which generates less power than they are potentially capable of producing at the given windspeed.
• flicker which often occurs in connection with wind power generation, i.e. voltage fluctuations which are typically due to periodical load variations.
• One of the manifestations of this phenomenon is a visual perception of electric lights flickering, which is, of course, unacceptable.
• Flicker caused by wind turbines usually lies within a frequency range of 0 - 8 Hz.
• the causes of flicker may vary: the blades passing through the lee of the windmill tower, periodic turbulence phenomena in the wind caused by particular types of terrain, trees growing near the windmill, etc. There is no currently known method of effectively suppressing or removing flicker from wind turbines.
• Grid quality refers to a set of required specifications - including a maximum grid-connection current, a narrow range of acceptable grid loads, a maximum permissible level of flicker, etc. - with which grid-connected wind power systems must comply before they can be approved.
• the purpose of this invention is to provide a solution to the problem of how to comply with power quality requirements. More specifically, the purpose is to provide a method to limit the grid-connection current of wind generators and to divert the surplus power generated in the 4
• the purpose of the invention is also to indicate a controllable electric brake load for the technique in the invention.
• the technique in the invention is distinctive in that the generator during the grid connection process - also at all times of operation when the generator yield is higher than desired with respect to grid compatibility - is loaded by a variable power diverter which is independent of the grid.
• This power diverter has a stepwise or continuously variable control system spanning a relatively wide output spectrum. The output interval chosen should be wide enough to enable a limitation of the power loaded onto the grid in order to keep the generator output from exceeding nominal grid design levels.
• This "dump-load” technique stabilizes the generator output to the grid at the maximum permissible yield without permitting it to exceed this level and without unnecessary waste of power that could otherwise be supplied to the grid.
• this technique ensures optimal yield as well as generator compliance with grid quality requirements
• the dump-load technique is thus used primarily in operational situations in which the windspeed varies in the interval between the turbine's nominal windspeed and the cut-out windspeed, plus in situations in which there are voltage fluctuations (flicker) which cause periodical surges in excess of the nominal voltage.
• the dump-load technique is also used, as mentioned above, during the process of connecting the generator to the grid, when the external dump-load serves as a supplemental load so that the turbine rotor can be effectively "reined in” during the connection process. This means that the turbine can be connected to the grid without power surges and without risk of it accelerating out of control.
• the dump-loader - which according to the inventions may consist of a resistor, capacitator or inductor or any combination thereof - is stepwise or continuously variable, i.e. can be connected in a stepwise or continuously variable manner via the generator by means of a thyristor switch or a similar electrical or electromechanical connection device of a known type (Claim 4).
• the dump-loader can dump all kinds of electric output, including capacitive and reactive power from the generator.
• the dump-loader functions as a resistor which is located directly above the generator and independent of the grid.
• control of the degree to which the dump-loader is connected may be made dependent on generator output and/or other relevant operating parameters which provide an indication of the generator yield.
• the control system can follow a preset program, e.g. in the form of an algorithm in one of the system's control computers.
• the program ensures that the dump-loader is disconnected when 5
• the generator yield is less than or equal to the nominal yield (i.e. grid design capacity).
• the nominal yield i.e. grid design capacity.
• power quality is taken into account (output spikes which exceed the nominal power threshold are "burned off' in the dump-loader) and utilization of the power generated by the turbine is optimized.
• the dump-load technique in the invention has the effect of stabilizing the generator output to the grid at the maximum permissible yield without exceeding it and without unnecessarily diverting power during times when the power could be delivered to the grid. In other words, the technique ensures an optimal yield while ensuring compliance with power quality requirements.
• Fig.1 is a curve which illustrates the operating conditions before, during and after the time a wind generator is connected to the grid
• Fig. 2 is a curve that shows the effect of the dump-load technique under operating conditions in which the generator yield exceeds the maximum permissible grid voltage
• Fig. 3 is a cross-section of windmill tower showing the location of the dump-load resistor elements.
• FIG 3 shows how the system's dump-load-resistor elements can be installed in the inside of the windmill tower (1 ), while the tower itself is utilized as a cooling surface.
• the tower consists of bent or rolled steel plate (2).
• the dump-load resistors - or, at least, their resistive components - consist of electric heat sinks (3) which sit in U-profile holders (4). These holders (4) are bolted tightly onto the interior of the tower plate.
• the heat from the power diverter is released into the tower plate and distributed along it, i.e. the tower plate functions as a cooling element.
• the heat sinks are symmetrically distributed along the outside of the tower, equidistant from each other, so that the temperature variation around the circumference of the tower is as low as possible.

Landscapes

• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Control Of Eletrric Generators (AREA)
• Supply And Distribution Of Alternating Current (AREA)
• Emergency Protection Circuit Devices (AREA)
• Protection Of Generators And Motors (AREA)

Applications Claiming Priority (3)

Publications (1)

Family

ID=8093549

Family Applications (1)

Country Status (6)

Families Citing this family (17)

Family Cites Families (3)

• 1998
  • 1998-03-30 DK DK199800438A patent/DK174466B1/da not_active IP Right Cessation
• 1999
  • 1999-03-30 JP JP2000541760A patent/JP2002510951A/ja active Pending
  • 1999-03-30 WO PCT/DK1999/000189 patent/WO1999050945A1/en not_active Application Discontinuation
  • 1999-03-30 EP EP99911642A patent/EP1097499A1/en not_active Withdrawn
  • 1999-03-30 AU AU30257/99A patent/AU3025799A/en not_active Abandoned
• 2000
  • 2000-09-29 NO NO20004889A patent/NO320903B1/no unknown

Non-Patent Citations (1)

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