CN106130076B - Low voltage ride through control method for self-sealing type electromagnetic coupling speed regulation wind turbine generator - Google Patents
Low voltage ride through control method for self-sealing type electromagnetic coupling speed regulation wind turbine generator Download PDFInfo
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- H02J3/386—
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- 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
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
- H02J3/40—Synchronising a generator for connection to a network or to another generator
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- 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
- H02P9/10—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load
- H02P9/102—Control effected upon generator excitation circuit to reduce harmful effects of overloads or transients, e.g. sudden application of load, sudden removal of load, sudden change of load for limiting effects of transients
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- 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
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- 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
- H02P2103/00—Controlling arrangements characterised by the type of generator
- H02P2103/20—Controlling arrangements characterised by the type of generator of the synchronous type
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- 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
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- 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
- Y02E10/76—Power conversion electric or electronic aspects
Abstract
The invention provides a low voltage ride through control method for a self-closed electromagnetic coupling speed regulation wind turbine generator, which solves the problem that the existing double-fed and full-power conversion wind turbine generators are different in grid-connected interface compared with synchronous generator sets in conventional power plants. The invention provides a low voltage ride through control method for a self-sealing type electromagnetic coupling speed regulation wind turbine generator. The self-closed electromagnetic coupling speed-regulating wind turbine generator and the control method thereof avoid the possible pollution of the wind turbine generator to a power grid due to the connection of a frequency converter and the power grid, realize the unification of the wind turbine generator and a conventional power plant on a grid-connected interface, really realize the aim of 'power grid friendly' of the wind turbine generator, and are beneficial to promoting the further development of the clean energy of wind power.
Description
Technical Field
The invention relates to the field of wind power, in particular to a control method of a self-closed electromagnetic coupling speed regulation wind turbine generator.
Background
The current mainstream wind generating sets are double-fed type and full-power conversion type wind generating sets, and the double-fed type and full-power conversion type wind generating sets can enable the rotating speed of a wind wheel to change along with the change of the wind speed, so that the capability of capturing wind energy to the maximum extent is realized. However, with the increase of the proportion of wind power in the power grid, the requirement of the wind turbine generator set for supporting the voltage and frequency of the power grid is continuously increased, and in both aspects, the current wind power generation unit has defects compared with the conventional power generation unit.
In the aspect of grid voltage support, a generator stator in a double-fed wind turbine generator is directly connected with a grid, and the grid voltage drops to cause overcurrent of a stator and a rotor and overvoltage of a direct-current bus. Due to the fact that the capacity of a converter of the double-fed wind turbine generator is limited, the control capacity of the converter on the double-fed generator is insufficient, and therefore the double-fed wind turbine generator is very sensitive to faults such as grid voltage drop. In order to prevent overvoltage and overcurrent of a rotor of the doubly-fed generator and overvoltage of a direct-current bus of the converter, an effective method is to add a hardware Crowbar circuit, once the Crowbar is put into use, the converter on the rotor side loses the capability of actively controlling the current of the rotor, the doubly-fed generator operates as a squirrel-cage asynchronous motor, and the converter does not have the capability of independently controlling the output active power and the reactive power of the wind turbine generator. At the moment, the wind turbine generator cannot generate reactive power to support the voltage of the power grid, and certain reactive power is absorbed from the power grid due to the need of excitation of the generator. For a full-power conversion type wind turbine generator, a back-to-back converter isolates a generator from a power grid, so that the low-voltage ride through capability of the wind turbine generator is superior to that of a double-fed wind turbine generator. When the voltage of the power grid drops, the grid-side converter sends reactive power to the power grid to support the voltage of the power grid, and the direct-current bus unloading resistor is put into use to consume redundant energy accumulated on the direct-current side so as to prevent overvoltage of the direct-current bus. Nevertheless, since the power electronic switching device is very sensitive to overvoltage and overcurrent, which may cause damage to the switching device in a short time, the overload capability of the power electronic switching device is very limited compared to that of a synchronous generator, which makes it difficult for the reactive power generated by the doubly-fed and full-power conversion wind turbine generators to support the grid voltage when the grid voltage drops.
The reason for the above problem is that the existing double-fed and full-power conversion type wind turbine generators are different in grid-connected interface compared with the synchronous generator set in the conventional power plant, and the grid-connected interface of the two wind turbine generators is no longer a synchronous generator, and in essence, the two wind turbine generators are current control type power supplies and the synchronous generator set is a voltage control type power supply.
Disclosure of Invention
In order to solve the defects in the prior art, the invention provides a low voltage ride through control method for a self-closed type electromagnetic coupling speed regulation wind turbine generator, wherein a grid-connected interface of the wind turbine generator is an electrically excited synchronous generator, a self-closed type electromagnetic coupling speed regulation device is connected with a high-speed shaft of a gear box and a rotor shaft of the synchronous generator, and power is transmitted from the gear box side to the synchronous generator side.
The technical scheme of the invention is realized as follows:
a low voltage ride through control method for a self-closed electromagnetic coupling speed regulation wind turbine generator adopts a self-closed electromagnetic coupling speed regulation device to connect a high-speed shaft of a gear box and a rotor shaft of an electrically excited synchronous generator, so that power is transmitted from the side of the gear box to the side of the electrically excited synchronous generator, and a grid-connected interface is the electrically excited synchronous generator;
the self-closed electromagnetic coupling speed regulating device consists of an electromagnetic coupler, a frequency converter and a permanent magnet synchronous generator, wherein the permanent magnet synchronous generator is used for supplying power to the frequency converter; the electromagnetic coupler is provided with two rotating shafts which are respectively connected with the gear box and the electrically excited synchronous generator and rotate, and the frequency converter controls the relative rotating speed and the electromagnetic torque of the two rotating shafts of the electromagnetic coupler;
the high-speed shaft of the gearbox is connected with one shaft of the electromagnetic coupler to form a front shaft system, the other shaft of the electromagnetic coupler is connected with a rotor shaft of the electrically excited synchronous generator to form a rear shaft system, the front shaft system and the rear shaft system are 2 independent shaft systems, and the permanent magnet synchronous generator and the front shaft system are coaxial to supply power to the frequency converter;
firstly, entering a starting process; after the starting process is finished, the electrically excited synchronous generator is excited, and the wind turbine generator is switched to a synchronous grid connection process; the method comprises the following steps of capturing wind energy to the maximum extent and stopping the machine set after grid connection;
once the voltage of a power grid falls and exceeds a normal range, the control of the self-closed electromagnetic coupling speed regulation wind turbine generator set is switched into a low-voltage ride-through control mode, the frequency converter is powered by a permanent magnet synchronous generator coaxial with a high-speed shaft of a gearbox, the falling of the voltage of the power grid cannot influence the power supply of the frequency converter, and in order to keep the output active current of the generator set constant, the torque instruction value T of the frequency convertercmd_LVRTThe calculation formula of (2) is as follows:
Tcmd_LVRT＝kTcmd(1)
where k is the per unit value of the grid voltage, TcmdThe method comprises the steps that a frequency converter torque instruction value is obtained by an optimal mechanical characteristic curve of a wind wheel when a self-closed electromagnetic coupling speed regulation wind turbine generator set basically runs, the pitch angle is obtained as the same as the pitch angle obtained when the voltage of a power grid is normal, and a PI regulator is used for obtaining the pitch angle according to a target value and an actual value of the rotating speed of the wind wheel;
after the voltage of the power grid is recovered, the exciting current of the electric excitation synchronous generator is gradually reduced, so that the reactive power generated by the wind turbine generator is recovered to the reactive power value generated before the voltage of the power grid drops.
Optionally, the starting process is divided into three phases:
firstly, in a first stage, the rotating speed of a wind wheel is gradually increased through variable pitch control, when the rotating speed of a front shafting is high enough, the output voltage of a permanent magnet synchronous generator meets the requirement of the power supply voltage of a frequency converter, the frequency converter is started and set to be in a rotating speed control mode, and an electromagnetic coupler is controlled through the frequency converter, so that the rear shafting is gradually accelerated to the rotating speed of a front shafting;
and then, entering a second stage, and controlling to synchronously rotate the front shafting and the rear shafting through a frequency converter until the set rotating speed value lower than the synchronous speed of the electric excitation synchronous generator is approached:
in the formula: n isIThe rotating speed of the front shafting; n isIIThe rotating speed of the rear shafting; n is1The synchronous speed of the electrically excited synchronous generator; f is the frequency of the power grid; p is the pole pair number of the electric excitation synchronous generator;
finally, entering a third stage, keeping the rotating speed of the front shafting unchanged by variable pitch control, and controlling the electromagnetic coupler through the frequency converter to enable the rear shafting to continuously increase the speed until the rotating speed is higher than the synchronous speed delta n of the electric excitation synchronous generator;
nII＝n1(1+Δn) (3)。
optionally, after the starting stage is completed, the electrically excited synchronous generator is excited, the wind turbine generator set is switched to a synchronous grid connection process, the grid connection control cabinet dynamically adjusts the exciting current and the frequency output by the frequency converter according to the amplitude difference and the phase difference between the voltage at the generator end of the electrically excited generator and the voltage of the power grid obtained through measurement, when the amplitude difference and the phase difference are reduced to a grid connection requirement allowable value, the grid connection switch is automatically switched on, and at this time, the frequency converter is switched to the torque control mode from the rotating speed control mode.
Optionally, after the wind turbine generator is connected to the grid, the output power of the electrically excited synchronous generator needs to be adjusted to a certain power suitable for the current wind condition, in the self-closed electromagnetic coupling speed regulation wind turbine generator, the power adjustment is completed by controlling the electromagnetic torque of the electromagnetic coupler through the frequency converter, and in order to reduce the impact of the loading and unloading processes of the electrically excited synchronous generator on the power grid, a slope function needs to be set in a power instruction for transition.
Optionally, when the wind speed is lower than the rated wind speed, the wind turbine generator operates in an under-power state, the pitch angle theta of the blades is kept near 0 degree, and the wind turbine generator adopts a maximum power point tracking strategy independent of wind speed measurement; the electromagnetic torque of the electromagnetic coupler is used as a control variable for adjusting the rotating speed of the wind wheel; obtaining a torque instruction value from a preset optimal mechanical characteristic curve of the wind wheel through table lookup according to the current wind wheel rotating speed, and handing the torque instruction value to a frequency converter to control the electromagnetic torque of an electromagnetic coupler;
when the wind speed is higher than the rated wind speed, the wind turbine generator operates in a constant power state; at the moment, the electromagnetic torque of the electromagnetic coupler is maintained at a rated torque value, and the rotating speed of the wind wheel is kept near the rated rotating speed by variable pitch control;
when the wind turbine generator is normally disconnected from the power grid, firstly, the electromagnetic torque of the electromagnetic coupler is gradually reduced, the load of the electric excitation synchronous generator is removed, and after the no-load state is reached, a grid-connected switch in a grid-connected control cabinet is disconnected; and after the wind turbine generator is disconnected, the frequency converter is switched from a torque control mode to a rotating speed control mode.
Optionally, the shutdown process is divided into 2 phases:
firstly, the rotating speed of a front shafting is kept at the rotating speed when a grid-connected switch is switched off through variable pitch control, and an electromagnetic coupler is controlled through a frequency converter to realize electromagnetic braking so that a rear shafting is decelerated to be equal to the rotating speed of the front shafting; and then, the rotating speed of the wind wheel is gradually reduced through variable pitch control, when the rotating speed is high enough to enable the frequency converter to be capable of normally supplying power, the front shaft system and the rear shaft system of the electromagnetic coupler are controlled to synchronously rotate, when the rotating speed is too low, the frequency converter stops working, the rear shaft system depends on friction braking torque, and the front shaft system depends on feathering control to finally complete the shutdown of the wind turbine generator.
The invention has the beneficial effects that:
(1) the self-closed electromagnetic coupling speed regulation device is connected with a gearbox high-speed shaft and an electrically excited synchronous generator rotor shaft, power transmission is realized, the frequency converter is connected with a permanent magnet synchronous generator coaxial with the gearbox high-speed shaft, normal application of the frequency converter to electromagnetic torque of the electromagnetic coupler during voltage drop of a power grid and black start of the wind turbine generator are realized, possible pollution of the wind turbine generator to the power grid due to connection of the frequency converter and the power grid is avoided, unification of the wind turbine generator and a conventional power plant on a grid-connected interface is realized, the aim of 'power grid friendly' of the wind turbine generator is truly realized, and further development of wind power, which is a clean energy source, is facilitated;
(2) the gear box is in non-contact connection with the electric excitation synchronous generator, so that the gear box is subjected to small mechanical impact from the side of the electric excitation synchronous generator, and the service life is prolonged;
(3) the rotating speed and the torque of the electromagnetic coupler are controlled through the frequency converter, and the response speed is high;
(4) the shaft rotating speed of the electromagnetic coupler gear box side is always lower than that of the electrically excited synchronous generator side, and the power flowing through the frequency converter is only a small part of the output power of the wind turbine generator and flows in a single direction, so that the frequency converter only needs to be operated in a single quadrant with smaller capacity.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is a schematic structural diagram of a self-sealing type electromagnetic coupling speed regulation wind turbine generator set according to the present invention;
fig. 2 is a schematic structural diagram of the self-sealing type electromagnetic coupling speed regulating device of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Compared with a synchronous generator set in a conventional power plant, the double-fed type and full-power conversion type wind turbine generators are different in grid-connected interface, and the grid-connected interfaces of the two wind turbine generators are not synchronous generators, so that the two wind turbine generators are current control type power supplies and the synchronous generator set is a voltage control type power supply.
The invention provides a self-closed electromagnetic coupling speed regulation wind turbine generator, wherein a grid-connected interface of the wind turbine generator is an electrically excited synchronous generator, and a self-closed electromagnetic coupling speed regulation device is connected with a high-speed shaft of a gear box and a rotor shaft of the electrically excited synchronous generator, so that power is transmitted from the gear box side to the electrically excited synchronous generator side, and the integration of the wind turbine generator and a conventional power plant on the grid-connected interface is realized.
The self-sealing type electromagnetic coupling speed regulation wind turbine generator set is described in detail below with reference to the accompanying drawings of the specification.
As shown in fig. 1 and fig. 2, the self-sealing type electromagnetic coupling speed regulation wind turbine generator set of the present invention adopts a self-sealing type electromagnetic coupling speed regulation device to connect a gearbox high speed shaft and an electrically excited synchronous generator rotor shaft, and realizes power transmission. The self-sealing electromagnetic coupling speed regulating device consists of an electromagnetic coupler 4, a frequency converter 6 and a permanent magnet synchronous generator 3, wherein the permanent magnet synchronous generator 3 is used for supplying power to the frequency converter 6. The electromagnetic coupler 4 is essentially a squirrel cage asynchronous machine, and is different from a common squirrel cage machine in that the electromagnetic coupler is provided with two rotating shafts which are respectively connected with the gear box 2 and the electrically excited synchronous generator 5 and rotate, and the frequency converter 6 controls the relative rotating speed and the electromagnetic torque of the two shafts of the electromagnetic coupler 4.
The high-speed shaft of the gear box 2 is connected with one shaft of the electromagnetic coupler 4 to form a front shaft system, the other shaft of the electromagnetic coupler 4 is connected with a rotor shaft of the electrically excited synchronous generator 5 to form a rear shaft system, the front shaft system and the rear shaft system are 2 independent shaft systems, and the permanent magnet synchronous generator 3 and the front shaft system are coaxial to supply power to the frequency converter 6. Compared with a power supply mode of supplying electric energy to the frequency converter 6 from power supply of a power grid, the power supply mode provided by the invention not only realizes normal application of electromagnetic torque of the frequency converter on the electromagnetic coupler during voltage drop of the power grid and black start of the wind turbine generator set, but also avoids possible pollution of the wind turbine generator set to the power grid due to connection of the frequency converter and the power grid.
The gear box 2 is in non-contact connection with the electric excitation synchronous generator 5, so that the gear box 2 is subjected to small mechanical impact from the side of the electric excitation synchronous generator 5, and the service life is prolonged; the rotating speed and the torque of the electromagnetic coupler 4 are controlled through the frequency converter 6, and the response speed is high; the shaft rotating speed of the electromagnetic coupler gear box side is always lower than that of the electrically excited synchronous generator side, and the power flowing through the frequency converter is only a small part of the output power of the wind turbine generator and flows in a single direction, so that the frequency converter only needs to be operated in a single quadrant with smaller capacity.
The self-closed electromagnetic coupling speed regulation wind turbine generator set has front and back 2 independent shafting, and firstly enters a starting process as shown in figures 1 and 2; after the starting process is finished, the electrically excited synchronous generator is excited, and the wind turbine generator is switched to a synchronous grid connection process; and the wind energy is captured to the maximum extent after the unit is connected to the grid, and the unit is stopped.
Once the voltage of the power grid falls and exceeds the normal range, the control of the self-closed electromagnetic coupling speed regulation wind turbine generator set is switched into a low-voltage ride-through control mode, and the power grid electricity is supplied by a permanent magnet synchronous generator coaxial with a high-speed shaft of a gearbox as a frequency converterThe voltage drop does not influence the power supply of the frequency converter, and the torque command value T of the frequency converter is used for keeping the output active current of the unit constantcmd_LVRTThe calculation formula of (2) is as follows:
Tcmd_LVRT＝kTcmd(1)
where k is the per unit value of the grid voltage, TcmdThe method comprises the steps that a frequency converter torque instruction value is obtained by an optimal mechanical characteristic curve of a wind wheel when a self-closed electromagnetic coupling speed regulation wind turbine generator set basically runs, the pitch angle is obtained as the same as the pitch angle obtained when the voltage of a power grid is normal, and a PI regulator is used for obtaining the pitch angle according to a target value and an actual value of the rotating speed of the wind wheel;
after the voltage of the power grid is recovered, the exciting current of the electric excitation synchronous generator is gradually reduced, so that the reactive power generated by the wind turbine generator is recovered to the reactive power value generated before the voltage of the power grid drops.
The self-closed electromagnetic coupling speed regulation wind turbine generator set generates corresponding reactive power to support the power grid voltage through the regulation of the exciting current of the electric excitation synchronous generator during the voltage drop of the power grid, and particularly when the power grid voltage drops seriously, the electric excitation synchronous generator has strong overload capacity, and the self-closed electromagnetic coupling speed regulation wind turbine generator set generates enough reactive power to effectively support the power grid voltage through the forced excitation operation of the electric excitation synchronous generator. After the voltage of the power grid is recovered, the exciting current of the electric excitation synchronous generator is gradually reduced, so that the reactive power generated by the wind turbine generator is recovered to the reactive power value generated by the wind turbine generator before the voltage of the power grid drops.
The starting process of the self-closed electromagnetic coupling speed regulation wind turbine generator set is different from that of other wind turbine generators, and can be divided into 3 stages:
firstly, in a first stage, the rotating speed of a wind wheel 1 is gradually increased through variable pitch control, the output voltage of a permanent magnet synchronous generator can meet the requirement of the power supply voltage of a frequency converter when the rotating speed of a front shafting is high enough, the frequency converter is started and set to be in a rotating speed control mode, and an electromagnetic coupler is controlled through the frequency converter, so that the rear shafting is gradually accelerated to the rotating speed of the front shafting;
and then, entering a second stage, and controlling the front and rear 2 shafting to synchronously rotate like a single rigid shafting through a frequency converter until the set rotating speed value lower than the synchronous speed of the electric excitation synchronous generator is approached:
in the formula: nI is the rotating speed of the front shafting; n isIIThe rotating speed of the rear shafting; n is1The synchronous speed of the electrically excited synchronous generator; f is the frequency of the power grid; p is the pole pair number of the electrically excited synchronous generator.
And finally, the rotating speed of the front shafting is kept unchanged through variable pitch control, and the electromagnetic coupler is controlled through the frequency converter to enable the rear shafting to continuously increase the speed until the rotating speed is higher than the synchronous speed delta n of the electric excitation synchronous generator (0< delta n < 5%).
nII＝n1(1+Δn) (3)
After the starting stage is completed, the electric excitation synchronous generator is excited, and the wind turbine generator set is switched to a synchronous grid connection process. And the grid-connected control cabinet dynamically adjusts the exciting current and the frequency output by the frequency converter according to the amplitude difference and the phase difference between the terminal voltage of the electric excitation synchronous generator and the grid voltage, which are obtained through measurement, and when the amplitude difference and the phase difference are reduced to the allowable value required by grid connection, the grid-connected switch is automatically switched on. At this time, the inverter is switched from the rotational speed control mode to the torque control mode.
After the wind turbine generator is connected to the grid, the output power of the electrically excited synchronous generator needs to be adjusted to a certain power suitable for the current wind condition. In the self-closed electromagnetic coupling speed regulation wind turbine generator, power regulation is completed by controlling electromagnetic torque of an electromagnetic coupler through a frequency converter. In order to alleviate the impact of the loading and unloading process of the electrically excited synchronous generator on the power grid, a reasonable ramp function needs to be set in the power instruction for transition.
When the wind speed is lower than the rated wind speed, the wind turbine generator operates in an underpower state, and the pitch angle theta of the blades is kept near 0 degree. In order to absorb as much wind energy as possible, wind turbines employ a maximum power point tracking strategy that does not rely on wind speed measurements. The electromagnetic torque of the electromagnetic coupler is used as a control variable for adjusting the rotating speed of the wind wheel. According to the current wind wheel rotating speed, obtaining a torque instruction value from a preset wind wheel optimal mechanical characteristic curve through table lookup, and handing the torque instruction value to a frequency converter to control the electromagnetic torque of an electromagnetic coupler.
When the wind speed is higher than the rated wind speed, the wind turbine generator operates in a constant power state. At this time, the electromagnetic torque of the electromagnetic coupler is maintained at the rated torque value. And the rotating speed of the wind wheel is kept near the rated rotating speed by the variable pitch control.
When the wind turbine generator is normally disconnected from the power grid, firstly, the electromagnetic torque of the electromagnetic coupler is gradually reduced, the load of the electric excitation synchronous generator is removed, and after the no-load state is reached, the grid-connected switch in the grid-connected control cabinet is disconnected. And after the wind turbine generator is disconnected, the frequency converter is switched from a torque control mode to a rotating speed control mode.
The shutdown process is divided into 2 phases. Firstly, the rotating speed of a front shafting is kept at the rotating speed when a grid-connected switch is switched off through variable pitch control, and an electromagnetic coupler is controlled through a frequency converter to realize electromagnetic braking so that a rear shafting is decelerated to be equal to the rotating speed of the front shafting; and then, the rotating speed of the wind wheel is gradually reduced through variable pitch control, when the rotating speed is high enough to enable the frequency converter to be capable of normally supplying power, the front shaft system and the rear shaft system of the electromagnetic coupler are controlled to synchronously rotate, when the rotating speed is too low, the frequency converter stops working, the rear shaft system depends on friction braking torque, and the front shaft system depends on feathering control to finally complete the shutdown of the wind turbine generator.
The self-closed electromagnetic coupling speed regulation wind turbine generator adopts a self-closed electromagnetic coupling speed regulation device to connect a gearbox high-speed shaft and an electrically excited synchronous generator rotor shaft and realize power transmission, the frequency converter is connected with a permanent magnet synchronous generator coaxial with the gearbox high-speed shaft, the normal application of the frequency converter to the electromagnetic torque of the electromagnetic coupler and the black start of the wind turbine generator are realized during the voltage drop of a power grid, the possible pollution of the wind turbine generator to the power grid due to the connection of the frequency converter and the power grid is avoided, the unification of the wind turbine generator and a conventional power plant on a grid-connected interface is realized, the aim of 'friendly power grid' of the wind turbine generator is really realized, and the further development of clean energy of wind turbine is facilitated.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.
Claims (6)
1. A low voltage ride through control method for a self-sealing type electromagnetic coupling speed regulation wind turbine generator is characterized in that a self-sealing type electromagnetic coupling speed regulation device is adopted to be connected with a high-speed shaft of a gear box and a rotor shaft of an electrically excited synchronous generator, so that power is transmitted from the gear box side to the electrically excited synchronous generator side, and a grid-connected interface is the electrically excited synchronous generator;
the self-closed electromagnetic coupling speed regulating device consists of an electromagnetic coupler, a frequency converter and a permanent magnet synchronous generator, wherein the permanent magnet synchronous generator is used for supplying power to the frequency converter; the electromagnetic coupler is provided with two rotating shafts which are respectively connected with the gear box and the electrically excited synchronous generator and rotate, and the frequency converter controls the relative rotating speed and the electromagnetic torque of the two rotating shafts of the electromagnetic coupler;
the high-speed shaft of the gearbox is connected with one shaft of the electromagnetic coupler to form a front shaft system, the other shaft of the electromagnetic coupler is connected with a rotor shaft of the electrically excited synchronous generator to form a rear shaft system, the front shaft system and the rear shaft system are 2 independent shaft systems, and the permanent magnet synchronous generator and the front shaft system are coaxial to supply power to the frequency converter;
firstly, entering a starting process; after the starting process is finished, the electrically excited synchronous generator is excited, and the wind turbine generator is switched to a synchronous grid connection process; the method comprises the following steps of capturing wind energy to the maximum extent and stopping the machine set after grid connection;
once the voltage of a power grid falls and exceeds a normal range, the control of the self-closed electromagnetic coupling speed regulation wind turbine generator set is switched into a low-voltage ride-through control mode, the frequency converter is powered by a permanent magnet synchronous generator coaxial with a high-speed shaft of a gearbox, the falling of the voltage of the power grid cannot influence the power supply of the frequency converter, and in order to keep the output active current of the generator set constant, the torque instruction value T of the frequency convertercmd_LVRTThe calculation formula of (2) is as follows:
Tcmd_LVRT＝kTcmd(1)
where k is the per unit value of the grid voltage, TcmdThe method comprises the steps that a frequency converter torque instruction value is obtained by an optimal mechanical characteristic curve of a wind wheel when a self-closed electromagnetic coupling speed regulation wind turbine generator set basically runs, the pitch angle is obtained as the same as the pitch angle obtained when the voltage of a power grid is normal, and a PI regulator is used for obtaining the pitch angle according to a target value and an actual value of the rotating speed of the wind wheel;
after the voltage of the power grid is recovered, the exciting current of the electric excitation synchronous generator is gradually reduced, so that the reactive power generated by the wind turbine generator is recovered to the reactive power value generated before the voltage of the power grid drops.
2. The low voltage ride through control method for the self-sealing type electromagnetic coupling speed regulation wind turbine generator set according to claim 1, wherein the starting process is divided into three stages:
firstly, in a first stage, the rotating speed of a wind wheel is gradually increased through variable pitch control, when the rotating speed of a front shafting is high enough, the output voltage of a permanent magnet synchronous generator meets the requirement of the power supply voltage of a frequency converter, the frequency converter is started and set to be in a rotating speed control mode, and an electromagnetic coupler is controlled through the frequency converter, so that the rear shafting is gradually accelerated to the rotating speed of a front shafting;
and then, entering a second stage, and controlling to synchronously rotate the front shafting and the rear shafting through a frequency converter until the set rotating speed value lower than the synchronous speed of the electric excitation synchronous generator is approached:
in the formula: n isIThe rotating speed of the front shafting; n isIIThe rotating speed of the rear shafting; n is1The synchronous speed of the electrically excited synchronous generator; f is the frequency of the power grid; p is the pole pair number of the electric excitation synchronous generator;
finally, entering a third stage, keeping the rotating speed of the front shafting unchanged by variable pitch control, and controlling the electromagnetic coupler through the frequency converter to enable the rear shafting to continuously increase the speed until the rotating speed is higher than the synchronous speed delta n of the electric excitation synchronous generator;
nII＝n1(1+Δn) (3)。
3. the low voltage ride through control method for the self-sealing electromagnetic coupling speed regulation wind turbine generator set according to claim 1, characterized in that after the start-up phase is completed, the electrically excited synchronous generator is excited, the wind turbine generator set is switched to a synchronous grid connection process, the grid connection control cabinet dynamically adjusts the exciting current and the frequency output by the frequency converter according to the measured amplitude difference and phase difference between the generator terminal voltage of the electrically excited generator and the grid voltage, and when the amplitude difference and the phase difference are reduced to a grid connection required allowable value, the grid connection switch is automatically switched on, and at this time, the frequency converter is switched from a rotation speed control mode to a torque control mode.
4. The method as claimed in claim 3, wherein after the wind turbine is connected to the grid, the output power of the electrically excited synchronous generator needs to be adjusted to a power suitable for the current wind conditions, and in the self-closed electromagnetically coupled speed-adjustable wind turbine, the power adjustment is performed by controlling the electromagnetic torque of the electromagnetic coupler through the frequency converter, and in order to reduce the impact of the loading and unloading processes of the electrically excited synchronous generator on the power grid, a ramp function needs to be set in the power command for transition.
5. The low voltage ride through control method for the self-sealing type electromagnetic coupling speed regulation wind turbine generator set according to claim 4, characterized in that when the wind speed is lower than the rated wind speed, the wind turbine generator set operates in an underpower state, the blade pitch angle θ is kept near 0 degree, and the wind turbine generator set adopts a maximum power point tracking strategy which is independent of wind speed measurement; the electromagnetic torque of the electromagnetic coupler is used as a control variable for adjusting the rotating speed of the wind wheel; obtaining a torque instruction value from a preset optimal mechanical characteristic curve of the wind wheel through table lookup according to the current wind wheel rotating speed, and handing the torque instruction value to a frequency converter to control the electromagnetic torque of an electromagnetic coupler;
when the wind speed is higher than the rated wind speed, the wind turbine generator operates in a constant power state; at the moment, the electromagnetic torque of the electromagnetic coupler is maintained at a rated torque value, and the rotating speed of the wind wheel is kept near the rated rotating speed by variable pitch control;
when the wind turbine generator is normally disconnected from the power grid, firstly, the electromagnetic torque of the electromagnetic coupler is gradually reduced, the load of the electric excitation synchronous generator is removed, and after the no-load state is reached, a grid-connected switch in a grid-connected control cabinet is disconnected; and after the wind turbine generator is disconnected, the frequency converter is switched from a torque control mode to a rotating speed control mode.
6. The low voltage ride through control method for the self-sealing type electromagnetic coupling speed regulation wind turbine generator set according to claim 1, wherein the shutdown process is divided into 2 stages:
firstly, the rotating speed of a front shafting is kept at the rotating speed when a grid-connected switch is switched off through variable pitch control, and an electromagnetic coupler is controlled through a frequency converter to realize electromagnetic braking so that a rear shafting is decelerated to be equal to the rotating speed of the front shafting; and then, the rotating speed of the wind wheel is gradually reduced by the variable pitch control, when the rotating speed is high enough to enable the frequency converter to normally supply power, the front shaft system and the rear 2 shaft systems of the electromagnetic coupler are controlled to synchronously rotate, when the rotating speed is too low, the frequency converter stops working, the rear shaft system depends on the friction braking torque, and the front shaft system depends on the variable pitch control to finally complete the shutdown of the wind turbine generator.
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| US4703189A (en) * | 1985-11-18 | 1987-10-27 | United Technologies Corporation | Torque control for a variable speed wind turbine |
| CN102155356A (en) * | 2011-03-22 | 2011-08-17 | 国电联合动力技术有限公司 | Method for controlling running of wind generating set based on speed-regulating front end of electromagnetic coupler |
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| US4703189A (en) * | 1985-11-18 | 1987-10-27 | United Technologies Corporation | Torque control for a variable speed wind turbine |
| CN102155356A (en) * | 2011-03-22 | 2011-08-17 | 国电联合动力技术有限公司 | Method for controlling running of wind generating set based on speed-regulating front end of electromagnetic coupler |
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