Smart power management during voltage dip in wind turbines

TECHNICAL FIELD The invention generally relates to wind turbines, and more particularly to a method of reducing mechanical loads by means of intelligent power management during voltage dips in wind turbines.

BACKGROUND ART [0002] A wind turbine converts kinetic energy of wind into electrical energy, which is then directed to a wind farm substation. Basically, in a wind turbine, the gondola houses the components together with the drive system for converting mechanical energy into electrical one. The propulsion system in a wind turbine usually means a rotor assembly, a rotor shaft, a gear, a generator shaft, a clutch and a generator. Wind turbines are designed to withstand various types of working conditions (normal operation, extreme gusts, loss of network, blocked shovel, etc.).

[0003] Nowadays the impact of wind turbines on the network is no longer negligible, so network operators impose more stringent requirements for connecting wind turbines to them. Some of these requirements are defined in terms of voltage dips that a wind turbine must be able to withstand without disconnection from the grid and the maximum time to resume power production after a failure.

[0004] The voltage dip scenario is one of the most difficult cases related to a wind turbine. The occurrence of voltage sags in the network is temporary and affects not only the electrical efficiency of the wind turbine, but also the mechanical one. In the event of a disturbance in the network, when the voltage drops below a certain value, it will reduce the wind turbine's power output due to electrical limitations. Since the dynamics of voltage dips is very fast, this reduction should be carried out very rapidly. The only way to achieve such a reduction in a short time is to reduce the moment of the generator. The torque dip stimulates the drive system in the range of its resonance frequency, leading to oscillation of the propulsion system. Given, that the aerodynamic moment remains unchanged (same wind speed and angle of attack), the speed of the generator increases as a result of the difference between the moment of the generator and the moment of the rotor. If the over-speed protection system is activated, the wind turbine is disconnected from the grid and stopped to meet the network operator's requirements. Consequently, the first goal is to limit the speed of the generator during the disturbance. This should be done without generating other alarms and maintaining a sufficient aerodynamic moment to obtain the previous production of power from before the collapse in a short time, imposed by the operator. the wind turbine is disconnected from the grid and stopped to meet the network operator's requirements. Consequently, the first goal is to limit the speed of the generator during the disturbance. This should be done without generating other alarms and maintaining a sufficient aerodynamic moment to obtain the previous production of power from before the collapse in a short time, imposed by the operator. the wind turbine is disconnected from the grid and stopped to meet the network operator's requirements. Consequently, the first goal is to limit the speed of the generator during the disturbance. This should be done without generating other alarms and maintaining a sufficient aerodynamic moment to obtain the previous production of power from before the collapse in a short time, imposed by the operator.

[0005] According to the above requirements, network operators not only define voltage dips that wind turbines must withstand, but also the maximum time to restore power production after the failure. As with any closed loop, the generator's torque control will show the maximum oscillations of coasting and damping before reaching steady state. This type of maximum momentum depends to a large extent on the way in which the control system provides the opportunity to regain moment in terms of the transmitted torque, but also the phase of oscillation at the natural frequency of the drive system that was excited by the rapid change of torque during the voltage dip. The momentary reaction of the system during the restoration of normal operation will depend on the logic control system.

[0006] Some control methods have been used in the past and have focused on changing the operation of the drive damper during voltage dips. This type of logic does not improve the way the generator torque and angles of attack are to meet the stabilization time requirements, minimizing the maximum overrun, or to integrate the drive system in the best possible way to ensure the best damping of the main propulsion frequency oscillation mode, or to improve cooperation between converter controller and wind turbine controller. In the next approach, a solution in the field of electrical design was provided, consisting in the use of a braking controller that reduces the coasting in the drive system. This method requires the installation of new wind turbine generators and additional costs.

SUMMARY OF THE INVENTION [0007] The above-mentioned drawbacks and problems will be solved with the following description.

[0008] The invention relates to a method for reducing the mechanical load during voltage dips in a wind turbine. A wind turbine with a propulsion system, a wind turbine generator, a wind turbine generator controller and a converter control unit. The wind turbine controller and the converter control unit work together to control the oscillation generated as a result of voltage dips in wind turbine 100. The method: Applies an optimal pitch reference value to minimize oscillations, avoid overspeed and maintain sufficient aerodynamic torque to restore production shortly after the failure. Applies a controlled incremental power reference value of different values ​​and filters it first to reduce the momentary range when recovering from the sag, thus meeting the requirements for stabilization time and integrating in the best possible way the operation of the propulsion damper. The method includes the stage of receipt by the wind turbine controller of information from the converter dipper control unit. In the next stage, the wind turbine controller calculates the current aerodynamic torque and the torque derivative against the angle of attack to obtain information on the remaining aerodynamic moment at any moment of the voltage dip, the minimum pitch is used to avoid excessive acceleration of the generator, maintaining the aerodynamic moment at the appropriate level to recover production after the collapse. When the voltage collapse stops, the maximum power or torque value is delivered by the converter control unit to the wind turbine controller. In terms of this type of temporary limitation, the wind turbine controller calculates a more stringent limit by subtracting the errors to ensure that it is possible to apply the DTD torque or the reference power value. The generator torque or power reference value is calculated using different values, depending on the propulsion oscillation, to minimize the momentary torque coast and to improve the oscillation mode of natural frequency of the propulsion system, taking into account the maximum power or value of the calculated torque and time constraints. The reference value is first filtered if necessary. At the end, an exact damping of the drive system is ensured at the rated pitch to provide additional damping of the oscillation mode of natural frequency of the propulsion system.

[0009] Further advantages will become apparent to those skilled in the art from the following description of preferred embodiments illustrating the best way to practice the invention.

DESCRIPTION OF THE DRAWINGS [0010] Preferred embodiments of the invention will be described with reference to the accompanying drawings, to illustrate and not to limit the invention, and wherein the same numbers designate the same elements:

Fig. 1 is a perspective view of a wind turbine according to an embodiment of the invention; Fig. 2 shows a side view of a gondola along a drive system according to the embodiment shown in Fig. 1;

Fig. 3 is a block diagram showing a method of communication between a wind turbine generator controller and a converter control unit for providing intelligent power or torque management according to an embodiment of the invention;

Fig. 4 shows the mode! a dual-mass torsion spring and damping of the wind turbine drive system shown in Fig. 1; and

Fig. 5 is a diagram showing the steps used in the method of reducing the mechanical load in a wind turbine according to an embodiment of the invention;

Figs. 6a and 6b show how the generator torque or power reference value differs after the voltage dip depending on the propulsion oscillation. When the oscillation is in the positive half of the plane, the value is higher.

Figures 7a-7c show the beneficial effects of using the invention at the time of voltage dip. DESCRIPTION OF THE PREFERRED EMBODIMENTS [0011] Although the invention may have several different forms to provide a better understanding of the principles of the invention, reference should be made to the preferred embodiments shown in the figures, to which the specific language will be used. The purpose of the description is not to limit the scope of the invention. Various modifications, changes to the described embodiments as well as further applications of the principles of the invention as described have been included.

[0012] The invention relates to a method for reducing the mechanical loads of a wind turbine during and after the failure of a voltage dip in a network without stopping. A wind turbine with a propulsion system, a wind turbine generator, a wind turbine generator controller and a converter control unit. The wind turbine controller and the converter control unit work together to minimize the oscillation generated as a result of voltage dips in wind turbine 100. Method: Applies an optimal pitch reference value to minimize oscillations, avoid overspeed and maintain sufficient aerodynamic torque to restore production shortly after the failure; uses a controlled incremental power value reference with different values ​​and filters it first, to reduce the range of the moment when coming out of the voltage sag, thus meeting the requirements for stabilization time and integrating in the best possible way the operation of the throttle of the drive unit. The method includes the stage of receipt by the wind turbine controller of information from the converter dipper control unit. In the next stage, the wind turbine controller calculates the current aerodynamic torque and the torque derivative against the angle of attack to obtain information on the remaining aerodynamic moment at any moment of the voltage dip, the minimum pitch is used to avoid excessive acceleration of the generator, maintaining the aerodynamic moment at the appropriate level to recover production after the collapse. When the voltage dip stops, the maximum power or torque value is delivered by the control unit 3 of the converter to the wind turbine controller. Due to this type of temporary constraint, the wind turbine controller calculates a more stringent limitation by subtracting the errors to ensure that it is possible to use the DTD reference torque ("propulsion damper"). The generator torque or power reference value is calculated using different values, depending on the oscillation of the propulsion system, to minimize the momentary range of torque and to improve the oscillation mode of natural frequency of the propulsion system, taking into account the maximum power or the value of the calculated torque and the stabilization time limit, This reference value is firstly filtered.

[0013] Fig. 1 is a perspective view of a wind turbine 100 according to an embodiment of the invention. The illustrated wind turbine 100 includes a tower 102 (hereinafter referred to as "tower") of a wind turbine, vertically positioned on foundation 104, a gondola 106 mounted on the upper end of the tower 102 and a rotor 108 mounted in the front of the nacelle 106 to provide its rotatable support around a substantially horizontal lateral axis of rotation Χ1-Χ 1. Rotor head 108 has a number of blades 110 of a wind turbine (e.g., three shown in Figure 1) mounted in a radial system about a rotation axis, thus wind power impinging on turbine blades 110. The rotor head 108 is converted into a drive power that rotates the rotor head 108 about the axis of rotation. The power that can be used, generated by the wind turbine 100, is led by the power line to the substation. At corresponding locations on the outer peripheral surface (e.g. at the top) of the nacelle 106, an anemometer (not shown) is provided which measures wind speed and an anemometer (not shown) which shows the wind direction.

[0014] Fig. 2 is a perspective side view of a nacelle 106 according to the invention as described in Fig. 1. Gondola 106 includes various components that form part of the wind turbine 100 drive system. Gondola 106 includes a rotor shaft 112, a gear 114, shaft 116 The generator, clutch 118 and wind turbine generator 120 (WTG) or generator 120. As a result of the movement of the blades 110 of the wind turbine, the rotor shaft 112 begins to rotate. The rotor shaft 112 extends to the transmission 114. The output shaft of the transmission 114 is called the generator shaft 116. The generator shaft 116 is connected to the receiving shaft 122 of the generator 120 via the coupling 118.

[0015] The wind turbine 100 further comprises a converter control unit 124 and a wind turbine controller 126 or a WGT controller 126. The converter control unit 124 and the WTG controller 126 are electrically connected to each other as shown in Fig. 3. The WTG controller 126 receives the signal from the converter control unit 124 and transmits the control signals back. The converter control unit 124 receives electrical measurements from various sensors and transmits a control signal to the electrical parts of the wind turbine 100. According to an embodiment of the invention, the converter control unit 124 and the WTG controller 126 cooperate to control the oscillation generated as a result of voltage dips in the wind turbine 100 Method: Applies an optimal jump reference value to minimize oscillations, avoid excessive speed and keep the aerodynamic moment sufficiently level to restore power output shortly after the failure. Applies a controlled incremental reference value of power of different values ​​and filters it first to reduce the range of the moment when coming out of the sag, thus meeting the requirements for stabilization time and integrating in the best possible operation of the throttle of the propulsion system.

[0016] When analyzing system stability, analyzing the system response to large interferences, the system generator shaft must be made using at least a dual mass model, as stated in Xing et al., "Damping Control Study of the Drive Train of DFiG Wind Turbina ", 2009. In this case, the system is a 100 wind turbine, and the occurrence of voltage dips in wind turbine 100 are disturbances.

[0017] Fig. 5 is a diagram 200 showing the steps used in the method of reducing the mechanical load in a wind turbine 100 according to an embodiment of the invention. At the beginning, in step 202, the WTG controller 126 receives information, the information is sent by the converter control unit 124. The information indicates the occurrence of voltage sags in wind turbine 100. The occurrence of voltage sag influences both the electrical and mechanical efficiency of the wind turbine 100. Before the voltage drop, the speed of the generator 120 is stable (controlled) and the transmitted moment Ti (aerodynamic moment) corresponds to a stable torque T generator₉. At the moment of voltage dip, it leads to a sudden change in generator torque. A sudden change in the generator's torque induces the drive system with the natural frequency, and the generator 120 accelerates as a result of the difference between Ti and T_g. At step 204, the WTG controller 126 calculates the aerodynamic moment and the torque derivative relative to the angle of attack to know the remaining aerodynamic moment at any moment of the voltage dip. In each computational step, the remaining moment can be estimated by subtracting from the initial aerodynamic moment at the beginning of the voltage dip, the result of multiplication of the torque derivative in terms of the angle of attack throughout the increment of the angle of attack from the moment of voltage dip. At step 206, the WTG controller 126 sends a command to the jump system 130 to override the neutral position at a predetermined speed to avoid excessive acceleration of the generator taking into account the remaining transferred torque Tt (aerodynamic moment). At this point, the main goal is to avoid an excessive speed alarm, but you must ensure a minimum possible return time after a failure. To do this, at the beginning of the dip, the command of the rate of change of stroke is calculated taking into account only the evolution of generator speed (velocity and acceleration) and physical limitations (limits of the jump system), as the dip progresses, the command of the pitch is calculated not only depending on previous coefficients, but also from the remaining transferred moment Ti. The contribution of each coefficient (generator speed, remaining moment transferred) can be estimated by using unit increments that multiply the maximum stroke determined by physical constraints. The weight of generator speed and acceleration coefficients is greater than the remaining transferred torque Tt, because the main purpose of this part of the voltage dip transmission is to avoid an over-speed alarm. The evolution of the remaining transferred moment Tt depends on the aerodynamics of the wind turbine and inertia of the rotor. As a reference value, it can be considered that this coefficient does not affect the evolution of the jump position as long as the transferred Tt moment does not fall below 80% of the initial value. On the other hand, as a reference value, if the generator speed is higher than 0.96%, the impact of the transferred Tt torque on the final reference value of the jump is skipping. that this coefficient does not affect the evolution of the jump position as long as the transferred moment Tt does not fall below 80% of the initial value. On the other hand, as a reference value, if the generator speed is higher than 0.96%, the impact of the transferred Tt torque on the final reference value of the jump is skipping. that this coefficient does not affect the evolution of the jump position as long as the transferred moment Tt does not fall below 80% of the initial value. On the other hand, as a reference value, if the generator speed is higher than 0.96%, the impact of the transferred Tt torque on the final reference value of the jump is skipping.

[0018] In step 208, the network returns after a voltage dip. The reference value of the stroke is calculated based on standard control rules. The converter control unit 124 calculates and transmits the maximum power or torque to the 126 WTG controller. The maximum active power can be calculated as the value of the maximum active power production multiplied by the mains voltage.

[0019] In step 210, the wind turbine controller calculates the maximum saturation setting for the active power or the torque reference value subtracting from the error the value coming from the converter control unit 124 to ensure that the reference torque reference value DTD can be used.

[0020] In a next step 212, the generator torque or power reference value is calculated using different values ​​depending on the oscillation (Figure 6) of the drive assembly to minimize the instantaneous torque ramp and to improve the oscillation mode of the propulsion system natural frequency, including maximum power or value of the calculated moment and limitation of the stabilization time. The reference value is first filtered if necessary.

[0021] Finally, in step 232, additional torque or active power of the drive damper (DTD) is added to the previous reference value derived from the last command sent to the converter control unit 124.

[0022] The use of the invention enables the wind turbine to continue to work without stopping in the event of a voltage dip, reducing the coasting of the drive system by more than 50% (Figure 7).

[0023] In an embodiment of the invention, the user can deactivate the algorithm by setting the parameter value from one to zero.

[0024] In an embodiment of the invention, the wind turbine 100 is a double-wind turbine 100. Wind turbines 100 double driven allow you to keep the output voltage of the generator and frequency constant. The dual-powered wind turbines 100 are subject to additional loads due to the need to withstand a voltage dip without disconnection. In a further embodiment, the wind turbine generator 120 uses full converter technology in which the voltage dip affects the drive system. It should be noted that the algorithm is also applicable to wind turbines with full converter technology without a braking controller. If the wind turbine generator 120 has a braking controller, it can compensate for the active power that the converter on the network side is unable to bring to the grid.

[0025] Any theory, mechanism of action, prototype or test results provided herein are intended to further improve the understanding of the principles of the invention and their purpose is not to make the invention dependent on such a theory, mechanism of operation, example, prototype or test results.

[0026] It should be remembered that although the use of the term "beneficial" in the description informs that the described function is more suitable, this is not necessarily the case, and the embodiments in which it is lacking are still within the scope of the invention as defined in the appended Claims, [0027] In the specification, the singular, the terms "at least one" or "at least part" do not limit the invention to the element only, unless the claims provide otherwise. The term "at least a part" and / or "a part" means that an element may comprise a part and / or the whole element, unless otherwise stated in the claims.

[0028] It should be remembered that only selected embodiments have been given and described and that all possible alternatives, modifications, aspects, combinations, bases, alterations or equivalents falling within the intention of the invention as defined herein or included in any of these The following claims are protected. Although the invention has been described and described in detail in the drawings and in the following description, it should be seen as exemplary and should not be regarded as exhaustive or limiting the invention to specific forms. Those skilled in the art will see many opportunities to make modifications and changes. In addition, despite the fact that many aspects and inventive principles can be presented,