Patent Application
20120286509
The present invention relates to a method for operating a wind turbine connected to a power grid for the electric energy generation when a change in a grid voltage occurs, and a wind turbine for implementing the method according to the present invention.
Wind turbines are commonly connected to the public power supply grid for the supply of the electric energy. In this power supply grid, voltage error or voltage deviation, for example, short circuit can occur, which results in a temporary decrease or also increase of the voltage in one or more phases. Conventional wind turbines will separate their connection to the grid after they recognize such a grid error and shut themselves off automatically. Such a shut off process of conventional wind turbines is described in
According to legal regulations of the different countries or regions, there exists the requirement for the wind turbines to maintain the energy production properly when an error of the power supply grid occurs. Especially for the situation in which the number of the wind turbines in the power supply grid increases, it is consequently required to modify the operation action of the wind turbines so that the arrangements ride through grid error and then support the reconstruction of the grid. For this purpose, different countries or regions have defined voltage limits, wherein the wind turbines may not be shut off until the voltage limits is undershoot. That is, when a deviation of a grid voltage or a grid error occurs in a range, which is above the defined voltage limit, the wind turbine should be still connected with the grid. Under the condition of certain voltage drop values, the arrangement should ride through the error or the state of the deviation of a grid voltage. This ride through is also described as “Low Voltage Ride Through” (LVRT). Herein, by means of characteristic lines depending on the current voltage value that deviates from the regular voltage range, it is given, how long the time period should be for further operating the wind turbine and/or in which operation state the wind turbine should be further operated. In the case of the grid voltage dip, the energy flow between wind turbines and grid changes itself, under certain conditions, less or no energy can be delivered to the power grid. The operation when riding through a variation of the grid voltage will be described as LVRT-operation in the following.
When normalizing grid voltage within the given time span, the wind turbine should also be in the regular operation again. However, if the deviation of the grid voltage or the grid error exists over the duration of the given time span, the wind turbine may be separated from the grid or be shut off.
Such kind of characteristic line for adjusting the dwell time in the grid depending on the respective voltage is described in
In one aspect, the operation of the wind turbine in the LVRT-operation is used to avoid the possible load states and error states of the turbine, which could be generated through the respective voltage dip. In another aspect, the operation of the wind turbine will be at least partly properly maintained, so as to prevent a complete collapse of the grid consequently and enable a rapid grid reconstruction.
Thus, the task of the present invention is to provided a method and a wind turbine to implement the method, with which the operation of the wind turbine can be maintained properly in a simple, time-and cost saving way when a deviation of the grid voltage occurs, and especially under the condition of keeping the given power drain and the given time frame, a complete collapse of the grid can be prevented and a rapid grid reconstruction can be guaranteed.
In order to solve the task, it is provided a method for operating a wind turbine connected to a power grid for the electric energy generation when a change in a grid voltage occurs, wherein the current residual grid voltage will be measured when a deviation of a grid voltage from a certain regular grid voltage range occurs, the current wind speed will be measured, a certain time period starting with the detection of the change in the grid voltage will be defined depending on the value of the residual grid voltage, and the wind turbine will be operated within the defined time period depending on the value of the residual grid voltage with a certain operation mode that deviates from the regular operation and the wind turbine will be operated again in the regular operation mode after the grid voltage has been normalized within the defined time period, or the wind turbine will be shut off at the end of the time period if the deviation of the grid voltage persists during the defined time period.
According to the present invention, it is set, that voltage ranges are defined for grid voltage values that are not included in the regular grid voltage range, wherein a plurality of voltage values and at least one first factor for controlling the wind turbine, which is optionally different for each voltage range, are attributed to each defined voltage range so as to realize the operation mode deviating from the regular operation mode, and depending on the measured wind speed, one of the first factors for controlling the wind turbine is used to realize the deviating operation mode.
The regular grid voltage range has a voltage lower limit, which usually will be undershoot when a voltage dips. Such a deviation of a grid voltage or a undershooting of the voltage limit should cause the adjustment of the changed operation. Thus, the deviation of a grid voltage can be understood as a voltage dip, that is, an error of the power supply grid, such as short circuit, for example, which will cause a temporary increase or decrease of the voltage in one or more phases.
The regular operation or the normalization of the grid voltage can be understood as the operation of the wind turbine, when no deviation of the grid voltage from the limit grid voltage range occurs. When measuring or recognizing a deviation from the regular grid voltage range, the wind turbine should be operated in a special operation mode, especially with reduced power, within a defined time period. If the deviation of the voltage exceeds the defined time period with regard to time, the wind turbine should be shut off. If the gird voltage is normalized again within the defined time span, the wind turbine should also further work again in the regular operation since this time point. Namely, when it is recognized or measured, that the grid deviation is ended, the wind turbine will be switched back to the mode of the regular operation again. This means, that there is a time span of the transition between the deviating operation mode and the regular operation since the switch to regular operation, in which all the adjustment to realize the regular operation are already essentially accomplished.
The method is used for the purpose that one and especially more wind turbines operated according to the present invention can ride through the grid error in LVRT operation when the grid error occurs. Wherein the wind turbines support the reconstruction of the grid through their latent complete readiness for operation and/or through their latent, even if reduced power drain, in the event that the grid error has been eliminated within a certain time period that is previously decided according to the effective determination. This mode for riding through the grid error will also named as LVRT-mode (Low Voltage Rid Through), wherein the wind turbine remains connected with the grid. If the grid error has not been eliminated within this time period, the wind turbine will be separated from the grid and shut off.
When a gird error occurs, a plurality of influencing variables influence the wind turbine, which should be further operated in a fully determined, given LVRT-operation that depends on the voltage drop. This influencing variable, for example, are the remaining residual grid voltage, the prescribed dwell time, which is derived from the remaining residual grid voltage, of the wind turbine in the grid and the dominant wind regime.
The almost continuous calculation of the suitable adjustment variables to realize the power reduced operation would either demand a relatively long time, during which the wind turbine does not correspond to the required operation conditions, or it requires a relatively high computation or control capacity.
In the context of the invention it is disclosed that factors for the adjustment of the wind turbine are attributed to current ranges which are deviated from the regular voltage range. Through using each of the first factors as control parameter respectively, the reaction to a voltage dip will be much more rapid, since only the factor, which is attributed to the voltage range, where the residual grid voltage is located, will be called, and used to control the wind turbine depending on, for example, the offsetting, wind speed.
Herein, it can be set, that the defined voltage ranges are overlaid with each other or abut against each other. Advantageously, they should be abut against each other, since additional suitable criteria for the selection of the respective range, and thus the effective factor in the overlapped range should be raised in the situation of the overlap of the defined voltage ranges.
Furthermore, it is set, that wind speed ranges will be defined, wherein a plurality of wind speeds are attributed to each defined wind speed range, and at least one second factor for controlling the wind turbine for each wind speed range will be attributed to each wind speed range, so as to realize the operation that deviates from the regular operation. Especially preferably, the second factor influences the power of the wind turbine.
Thus, an advantage is obtained, that the factors for the adjustment of the wind turbine are attributed to the wind speed ranges, and the reaction to the voltage dip will be much more rapid, since only the factor, which is attributed to the wind speed range, where the current wind speed or the turbine working point is located, will be called and used to control the wind turbine.
In order to further simplify and accelerate the determination of the adjustment value to realize the desired power, it is set that a control desired value for the operation of the wind turbine is generated from the combination of the first and second factors so as to adjust the operation mode that deviates from the regular operation. Herein, the first factor can be combined with the second factor, for example, computationally.
In order to influence the aerodynamic power of the wind turbine in a goal-oriented manner, it is set that the first and/or the second factor and/or the control desired value can used to influence the blade angle of the rotor blade of the wind turbine.
Through changing the blade angle—also named as pitch angel—of the rotor blade, the absorbed aerodynamic power, and thus the number of the rotor revolution also will be influenced in a simple way. Therefore, an overwinding of the wind turbine can be avoided when a voltage dip occurs. By the adjustment of the blade angel, the angel of attack of the wind turbine will be set so, that the blades will no longer be optimally blew and the rotor revolves slowly and/or the rotor moment is reduced, whereby the desired LVRT operation mode can be realized. From this operation mode, the wind turbine can be either restored very rapidly again to the regular operation mode or shut off.
When a voltage dip occurs, an aerodynamic rotor brake arrangement of the wind turbine will also no longer be supplied with enough electric energy, so that the wind turbine can no longer be braked if necessary. Herein, the adjustment of the blade angles enables battery operation under certain conditions, that is, it does not require grid voltage to adjust the blade angles, so that the blade angle can also be adjusted in an autarkic manner when a severe grid dip occurs.
In an especially preferable embodiment, the first factor can cause or be a control signal for a revolution number regulator, wherein the revolution number regulator cause the change of the blade angle. In other words, this means, that when a certain limit voltage is undershoot, the wind turbine will be operated in LVRT-operation and thus the certain values of the revolution number will be adjusted through the change of the blade angle. The increased load, for example, overwinding of the arrangement, will be avoided by the desired values of the revolution number that is given according to the operation mode and wind speed, and meanwhile the wind turbine will be maintained in operation, so as to be available during the grid reconstruction more rapidly and so as to avoid that the grid will not collapse during the grid error.
Advantageously, it is set, that the value of the current blade angle when a change in the grid voltage occurs will be obtained or called, and an offset angle value will be determined from the first and/or the second factor and/or the control desired value, or such an offset angle value, which is previously stored in a memory for a respective voltage range not included in the regular grid voltage range, will be called from the memory, and will be fed to a controller of the wind turbine for the purpose of intrusion on the current blade angle, and the blade angle will be correspondingly changed. Therefore, the blade angle adjustment is accomplished by taking account of the current blade angles when the deviation of the grid voltage occurs. Herein, the offset angle value can also be computationally determined.
Alternatively or additionally, it can be set, that a first factor and/or a control desired value are used to regulate the operation of a resistance unit. Such a resistance unit can be resistances of a rotor of an asynchronous generator with cage rotors or can also be a resistance in a direct current voltage intermediate circuit of a rotor of an double fed asynchronous generator. Herein, a resistance unit can include a switch, especially an IGBT-switch, and at least one or more resistance that current can go through. Therefore, the influence of the operation of the generator and/or under certain conditions a transformation from the generated electric energy to heat energy can be realized. This means, that a first factor can also be used to control the so-called duty circle. This means that the switch period and/or—frequency of the switch mentioned above, especially the IGBT-switch, and consequently the trigger of the resistance unit can be influenced.
Alternatively, it is possible, that the combination of the first factor with the second factor leads to a third factor, which is used to regulate the IGBT-switch and thus the resistance. At least one of the factors and/or the control desired value should be used to adjust the cable electronic system of the wind turbine. If necessary, the combination of the first factor with the second factor is a computational combination.
Therefore, the adjustment of the cable electronic system of the wind turbine can be realized to influence the operation mode of the wind turbine, because in this way the adjustment of the blade angle and/or the energization of the resistance unit can be conducted. Thus, unacceptable load state and/or error states for these systems caused by the voltage dip and/or possible voltage normalization are avoided.
To guarantee that the deviating operation mode will be carried out at least for a prescribed time period when a deviation of a gird voltage occurs, it is set, that the defined time period will be defined according to the highest voltage value of a defined grid voltage range.
As mentioned, a time window will be defined according to a given characteristic lines, within which the wind turbine can be operated in a LVRT-operation. Herein, according to the present invention, the time period will be defined according to the greatest voltage value for each selected range.
Since the characteristic line has a positive slope, the defined time period is at least just as long as the time period given through the characteristic line for the deviating operation.
In the context of the LVRT-operation of the wind turbine, alternatively or additionally to the measures mentioned above, a special trigger of apparatuses can be carried out, which does not influence the performance of the wind turbine directly, such as, for example, oil pump, fan, driving motor for the yaw system, namely all auxiliary motors, which will not be directly needed for the regulation of the revolution number of the rotor or resistance energization. Especially, these apparatus are shut off in the course of LVRT. This is essentially used for the operation assurance of the apparatuses for the time after the deviation of the grid, so as to protect the electrical system of the wind turbine from an undefined current impulse. Therefore, it can be additionally set, that through at least one of the factors and/or through the control desired variable, a time that is taken for influencing the operation manner of the wind turbine is longer than the determined time period or the time during which the deviation of the grid voltage occurs.
In order to maintain the grid in the case of a simultaneous option of shutting off the wind turbine rapidly, it is set, that the method is so developed, that the wind turbine generates less power in the operation mode deviating from the regular operation regarding the power than in the regular operation.
In order to minimize the calculation cost and thus the necessary time to implement the method, the method can be so implemented, that a respective first and/or second factor and/or control desired value attributed to the respective voltage range and/or wind range is defined and stored in at least one memory and is called therefrom for the adjustment when the deviation of the voltage corresponding to the respective factor and/or control desired value occurs. It means that tables are stored in the memory, and in these tables, the factors attributed to the ranges of at least one of the reference values voltage and wind speed are stored. Therefore, the factors and/or control desired value will be defined and stored before a deviation of a grid voltage occurs, so that when, for example, a grid error occurs, they can be used to control the wind turbine, especially to adjust the blade angle and/or the operation of the resistance unit.
Additionally, according to the invention, it is set, that at least one of the factors and/or the control desired value is used for the selection and trigger of wind turbine apparatuses, which are shut off during the time of the deviation of the grid or also operated in an operation mode which deviates from its regular operation mode. This means, that the existence or the amount of a factor or the control desired value determines which apparatus will be shut off during the grid error. Usually, they are those apparatuses, whose operation has no direct influence on the performance. Such kinds of apparatuses are, for example, oil pumps, fans and driving motors for the adjustment of the yaw system.
Additionally it can be set, that at least one of the factors and/or the control desired value is used to control the idle power during the deviation of the grid. Herein, the idle power can be adjusted by means of a compensation arrangement. Such a compensation arrangement can be a capacitor control box for the compensation of the idle power.
For the adjustment of the operation performance of the wind turbine after the end of the deviation of the grid, it can be set in the transition back to the regular operation, that at least one of the factors and/or the control desired value is used for the adjustment of parameters of the operation after the end of the deviation of the grid.
Herein, the produced parameter can exist as function, for example, that allows how soon it could be start again after the end of the error. Herein, according to the depth of the voltage dip and the time of the deviating operation mode, different start-up performance can be required.
Additionally, the method according to the present invention can be so developed, that at least one of the factors and/or the control desired value is used for the generation of parameters so as to adjust error suppression time. The error suppression time is used for the adjustment of the reaction delay of certain apparatuses of the wind turbine energized by the grid, thus that apparatuses will be switched on and/or shut off in a desired or required sequence.
Preferably, the method is so developed, that at least one of the factors and/or the control desired value is used for the generation of a maximal number of the repetition of the deviation of the grid within a second defined time span, wherein the wind turbine will be shut off when the maximal number has been exceeded. Moreover, the second defined time span is previously decided for each voltage range and for each wind strength if necessary.
The range of the deviation of the grid voltage can be divided to a first voltage range with greater than 90% of the regular grid voltage, to a second voltage range with 90-45% of the regular grid voltage, to a third voltage range with 44-22% of the regular grid voltage and to a fourth voltage range with 21-0% of the regular grid voltage. The first voltage range will be preferably interpreted as regular voltage range, in which the wind turbine will not be operated in the LVRT-mode.
Herein, it is set, that the certain time period of the realization of the deviating operation mode, beginning with the detection of the change in the grid voltage, is 0 second long in the first voltage range, and 2.5 seconds long in the second until the fourth voltage range respectively.
In the case of deviation from the required time period, which is 2,5 or 2,3 s in the second voltage range, 1,75 s in the third voltage range and 1,12 s in the fourth voltage range, the adjusted time of the deviating operation mode exceeds the required time in the third and fourth voltage range consequently, which although causes an extended operation period of the wind turbine, in another aspect allows an essentially simpler and thus rapider computation of the control parameter of the wind turbine.
The wind speed is divided to a first wind range with 4-7, a second wind range with 8-11, a third wind range with 12-14 and a fourth wind range with greater than 14 m/s.
In the case of the further deviation of the grid voltage, the method can be so implemented, that when a new change of the grid voltage occurs within the defined time period at a voltage value, which is not included in the voltage range corresponding to the initial deviation of the voltage, another first factor for controlling the wind turbine will be used to realize the operation mode which deviates from the regular operation mode.
This means, that in the case of the further voltage drop, another first factor will be generated or called other than the factor adjusted according to original voltage drop.
The similar situation is related to the control desired variable and the second factor if necessary, in the case of the correspondingly long measured time period for the operation in the deviating operation mode (LVRT), in which a repeated wind speed measure is meaningful.
In order to solve the task, additionally, a wind turbine, which is connectable or connected to a power grid to supply electric current, will be provided. The wind turbine according to the present invention include the following devices: at least one gird voltage measuring device, at least one wind speed measuring device, which can be also external positioned if necessary, at least one control device, set to realize a plurality of operation modes which deviate from the regular operation, and at least one first memory, in which first factors attributed to different grid voltage ranges are storable or stored. The wind turbine according to the present invention is especially developed for the implementation of the method according to the present invention.
Herein, it can be set, that the wind turbine additionally includes a second memory, wherein the second factors attributed to different wind speed ranges can be stored or are stored in the respective first and/or second memory.
In order to store the control desired value generated from the computational combination of the first or second factor, it can be set, that the wind turbine includes a third memory or that the first and/or second memory of the wind turbine is so developed, that the control desired values are storable or stored in them.
Alternatively or additionally, it can be set, that the wind turbine includes at least one computation unit, by means of which an offset-angle value can be calculated from the first and/or the second factor and/or the control desired value.
For the regulation of the effective power, the wind turbine includes at least one resistance unit, by means of which the operation performance of the wind turbine, especially of the generator can be influenced, wherein the electric energy generated from the wind turbine can be transformed to heat energy possibly for the purpose of the regulation of the effective power of the wind turbine. Additionally, the wind turbine can include at least one compensation arrangement, by means of which the idle power of the wind turbine can be adjusted.
Additionally, according to the present invention, a computer program is provided, that after it is loaded in a memory means of a data processing device, it enables the data processing device to implement the method for operating a wind turbine connected to a power grid for the electric energy generation when a change in a grid voltage occurs according to the present invention.
This means, the computer program enables at least the following steps or gives the corresponding control instructions: measuring the current residual grid voltage when the grid voltage deviates from a certain regular grid voltage range, measuring the current wind speed, defining a certain time period beginning with the detection of the change in the grid voltage depending on the value of the residual grid voltage, operating the wind turbine within the defined time period depending on the value of the residual grid voltage in a certain operation mode deviating from the regular operation regarding the effective power, operating the wind turbine again in the regular operation mode after the grid voltage has been normalized with the defined time period, or shutting off the wind turbine at the end of the time period if the deviation of the grid voltage persists during the defined time period, providing first factors for controlling the wind turbine, which are different for each voltage range, to realize the operation mode that deviates from the regular operation mode.
The invention relates to a computer readable memory medium, on which a program is stored, after the program is loaded in a memory means of a data processing device, it enables the data processing device to implement the method for operating a wind turbine connected to a power grid for the electric energy generation when a change in a grid voltage occurs according to the present invention.
Therefore, the invention also includes a method, wherein the computer program according to the present invention is downloaded from an electrical data network, for example, from the internet, to a data processing device connected to the data network.
The invention is also related to a method for controlling a wind turbine in the case of grid errors by means of tables. The grid errors will be classified according to regulations. This classification is suitable for predefined tables with operation parameters of the wind turbine. Some parameter can have availability, which is longer than the duration of the grid error. This is based on the step formation along the characteristic line.
The present invention will be described by means of the appended figures. In the drawing:
In the
In
The respective factors attributed to the voltage ranges 3.2 to 3.5 can be stored in the tables. In other tables, shut off period for the apparatuses, which must be shut off during the voltage dip, will be registered for each voltage range. The number of the step adjusts itself according to the current grid guide line, according to the computational device of the arrangement and according to the technical assemblies and according to the arrangement performance. In general, more fine stepped the range formation along the characteristic line is, more accurate the adjustment value of the wind turbine can be realized. Concerning the residual voltage and the dwell time defined by the residual voltage, the advantage of the steps or range formation are that control values are essentially provided without time delay and with any accuracy. Therefore, the relative long shut off time in the conventional manner in the case of the shut off of the wind turbine can be essentially shortened by approximate ¼ second. In the case of the further change of the voltage in the already available deviation of the grid voltage, it can react by switching to other table values.
The effectiveness of some table regulations goes beyond the grid error period based on the step formation described in
In
It is apparent, that the grid voltage 4.1 has taken the regular level again after a certain time 4.8. Hence, the signal about the measured grid voltage dip 4.2 ends. Hence, likewise, a new signal will be generated concerning an electric error 4.3. Therefore, by normalizing the grid voltage 4.1 within the time of the deviating operation manner 4.7 given by the characteristic line, the deviating operation manner, the LVRT-operation, 4.5 will be likewise ended, such that the wind turbine will be further operated in the regular operation again in the case of the normalization of the grid voltage. This means, that the shut off of the wind turbine does not need to be realized in the situation described in
On the contrary, the situation is described in
In the following, with respect to
The energy control device 6.3 includes one or more resistances 6.31, which are connected through a switch 6.34 (e.g. IGBT), wherein a rectifier 6.32 and an overvoltage protection 6.33 can be preferably configured between one or more resistances 6.31 and the switch 6.34. This IGBT-switch 6.34 is coupled with a first control unit 6.35. The first control unit 6.35 is likewise coupled with the control system 6.4, which has a so-called LVRT-controller 6.41, to which a grid voltage measuring device 6.42, and a protection device 6.43 and a blade angle device 6.43 is connected. A second control unit 6.46 is likewise coupled with the first control unit 6.35 and the control system 6.4, the second control unit 6.46 can influence an idle power element 6.45. The generator 6.2 is connected with the control system 6.4 through current cables 6.47 and voltage cables 6.48.
When a deviation of a grid voltage or a grid error occurs, the blade angle of the rotor blades 6.1 is changed through the first control unit 6.35 to realize the operation of the wind turbine in the operation manner which deviates from the regular operation mode, so as to realize the desired revolution number. Furthermore, the first control unit 6.35 can so trigger the IGBT-switch 6.34, that through this a change of the current feed of the resistance 6.31 will be implemented, so that the electric energy generated from the wind turbine is transformed to heat energy there and thus influences the effective power generated from the wind turbine. Alternatively, the control system 6.4 can also be used for changing of the blade angle of the rotor blades 6.1.
A revolution number controller and regulator 7.6 for controlling the blade angle adjustment system 7.61 and an inverter controller 7.8 for controlling the convert system 7.2, which are in turn connected with the control system 7.4 of the wind turbine, are set. The control system 7.4 measures the grid voltage.
The elements of the control system 7.4 not described in
>90%
The feature combinations disclosed in the described embodiments do not limit the scope of the invention, and the features of different embodiments can rather be combined with each other.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2009-027.981.4 | Jul 2009 | DE | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/60759 | 7/23/2010 | WO | 00 | 7/30/2012 |
