CONTROL STRUCTURE AND CONTROL METHOD FOR A WIND ENERGY PLANT

Description

[0001] The present invention relates to a controller structure for a wind turbine having an aerodynamic rotor with at least one rotor blade, an associated control method as well as a wind turbine and a wind farm.

[0002] Controller structures for operating wind turbines are well known. The most common are so-called pitch-controlled wind turbines, in which the rotor blades of the wind turbine's rotor are adjustable around their longitudinal axis, the so-called pitch axis. By changing the pitch angle, the aerodynamic performance of the rotor blades is changed, which allows the power to be limited to the nominal power when the nominal wind speed is reached. For this purpose, so-called speed controllers are known, as shown schematically in Fig. 2 shown, to provide a target speed N Target The speed controller 200 is designed to maintain the set speed N Targetas a reference variable if possible, whereby an actual speed measured by the wind turbine 100 N Is and the deviation is converted into a settable pitch rate by means of a P controller 210 and a D controller 220. The pitch rate is limited by a pitch rate limiter 230 to a target pitch rate 240, which is then used to operate the wind turbine 100.

[0003] The quality of speed control directly influences the cutting loads of important components of the wind turbine, such as the tower and the rotor blades.

[0004] The German Patent and Trademark Office has searched the following prior art in the priority application for the present application: DE 10062025 C1, DE 2903819 A1, DE 10213792 A1, DE 102017105165 A1, US 2014 / 0246855 A1, US 2015 / 0130187 A1, EP 2933477 B1.

[0005] Additionally, document US 2015 / 292483 A1 describes a system and method for dynamically controlling a wind turbine. The method includes operating the wind turbine based on a thrust setpoint and a speed setpoint. A next step includes determining a desired change in the actual speed of the wind turbine in response to control inputs from a current operating point. The method also includes determining a desired change in the thrust of the wind turbine in response to control inputs from the current operating point.Next, the method determines at least one parameter setpoint that achieves the desired change in speed and the desired change in thrust and controls the wind turbine based on the parameter setpoint so that the actual thrust and the actual speed of the wind turbine are maintained within a certain tolerance of the thrust setpoint and the speed setpoint in order to regulate the loads acting on the wind turbine while achieving near-optimal power output.

[0006] Given this prior art, it was an object of the present invention to provide a controller structure for speed control that enables a reduction of the loads of the wind turbine.

[0007] According to a first aspect, the object is achieved by a controller structure for a wind turbine according to claim 1.

[0008] Designing the speed control as a cascade control system enables the slow, outer speed control to be transformed into faster control by providing the inner control loop with a rapidly adjustable reference variable. This creates the basis for effectively reducing the loads acting on the wind turbine. In other words, the slow reference variable of the outer control loop is maintained, but the speed of the controller is compensated by a rapidly changing reference variable of the inner control loop.

[0009] In one embodiment, a controlled variable of the outer control loop is provided as the reference variable of the inner control loop. The manipulated variable of the outer control loop is therefore a speed change, a speed acceleration, a function of the speed change, and / or a function of the speed acceleration.

[0010] In one embodiment, the outer control loop is designed to limit a setpoint of the inner control loop, in particular the speed change, the speed acceleration, the speed change function, and / or the speed acceleration function. This advantageously allows for limiting the maximum acceleration acting on the rotor and the associated loads.

[0011] The input signal of the inner control loop comprises a rotor acceleration power or a rotor acceleration torque, wherein the rotor acceleration power or the rotor acceleration torque describes the part of a power or torque absorbed by the rotor of the wind turbine that is converted into an acceleration of the rotor.

[0012] Here and in the following, the terms "power" and "torque" are used interchangeably, as they can be easily converted using the simplest conversions based on the rotational speed. Therefore, descriptions and advantages explained with reference to a power output are also valid for the corresponding torque, and vice versa.

[0013] In one embodiment, the input signal of the inner control loop comprises an aerodynamic power absorbed by the rotor, wherein the aerodynamic power absorbed by the rotor comprises a sum of a rotor acceleration power and at least one power absorbed by another component of the wind turbine, in particular a generator power of a generator of the wind turbine, wherein the rotor acceleration power describes the part of a power absorbed by the rotor of the wind turbine that is converted into an acceleration of the rotor.

[0014] In one embodiment, the outer control loop determines a deviation of an actual speed of the rotor from a target speed of the rotor as a control deviation.

[0015] The outer control loop thus acts in accordance with a conventional speed control of the wind turbine, whereby the inventive design as a cascading control enables a significantly faster adjustment of the desired variables.

[0016] In one embodiment, the outer control loop generates a setpoint value for a power or torque as a manipulated variable. This power is preferably the acceleration power of the rotor or the absorbed aerodynamic power, respectively. Analogously, as mentioned, the analysis can be performed with the associated torques instead of powers.

[0017] The outer control loop preferably always generates the physical quantity as the setpoint that serves as the input signal for the inner control loop. This physical input signal generally includes a speed change, a speed acceleration, a function of the speed change, a function of the speed acceleration, a rotor acceleration power, a rotor acceleration torque, and / or an aerodynamic power.

[0018] In one embodiment, the power setpoint is limited both upwards and downwards. This prevents excessive regulation by the inner control loop, which could, for example, lead to excessive loads.

[0019] In one embodiment, the power setpoint is limited asymmetrically both upwards and downwards. This allows, for example, acceleration power to be limited to a different value than braking power, which in turn reduces the maximum loads that can occur.

[0020] In one embodiment, the power comprises a rotor acceleration power, wherein the rotor acceleration power is limited to a rated power of the wind turbine, in particular to a maximum of 20% of the rated power of the wind turbine. Limiting the rotor acceleration power prevents excessive load caused by acceleration.

[0021] In one embodiment, the power comprises an aerodynamic rotor power, wherein the aerodynamic rotor power is limited to twice the rated power of the wind turbine, in particular to a maximum of 120% of the rated power of the wind turbine. The aerodynamic rotor power comprises, in particular, the sum of the generator power and the rotor acceleration power.

[0022] In one embodiment, the inner control loop generates a pitch angle or a pitch angle change rate of at least one of the rotor blades as a control variable. The pitch angles or rates of change can be provided individually for each rotor blade or collectively for all rotor blades.

[0023] In one embodiment, the setpoint value of the rate of change of the pitch angle is limited, in particular to a value between -18° / s and 18° / s and particularly preferably to a value between -5° / s and +5° / s.

[0024] In one embodiment, the outer control loop and / or the inner control loop comprise a P-controller.

[0025] Particularly when a pitch angle is output as the setpoint, the inner control loop alternatively or additionally features an I controller. In particular, the controller can also be designed as a PI controller, which is particularly advantageous when the output is a blade angle instead of a pitch rate.

[0026] In one embodiment, the controller structure further comprises a calculation component configured to determine a rotor acceleration power from a change in a measured actual speed of the wind turbine using the rotor inertia.

[0027] In one embodiment, the controller structure further comprises a pilot control for pilot controlling a pitch angle of at least one rotor blade, which is configured to specify a pitch angle and / or a rate of change of the pitch angle in parallel to the inner control loop.

[0028] The aerodynamic target power or the target rotor acceleration enables the determination of a target blade angle or pitch angle, for example in order to be able to pre-steer before strong, impending gusts, which together with the actual blade angle or actual pitch angle are calculated to form a pre-steer pitch rate.

[0029] Preferably, both pitch rates—that is, the rate of change of the pitch angle due to the internal control loop and the rate of change of the pitch angle due to the feedforward control—run in parallel so that they overlap. It is then a matter of the design of the wind turbine to determine which of the two specified rates is implemented by the turbine and in what manner. The feedforward control provided in this aspect makes it possible to at least partially absorb extreme loads, such as those that occur particularly during gusts.

[0030] According to a further aspect, the object is achieved according to the invention by a method for operating a wind turbine according to claim 12.

[0031] The method according to the invention enables the same advantages to be achieved as described for the controller structure according to the invention. Likewise, the method can be combined analogously and with the associated advantages with the embodiments described as preferred according to the invention.

[0032] According to a further aspect, the object is achieved according to the invention by a wind turbine with a controller structure according to the invention.

[0033] According to a further aspect, the object is achieved according to the invention by a wind farm with several wind turbines according to the invention.

[0034] Further advantages and exemplary embodiments are described below with reference to the attached figures. Herein: Fig. 1 schematically and exemplarily shows a wind turbine, Fig. 2 schematically and exemplarily shows a controller structure for speed controllers of wind turbines and Fig. 3 schematically and exemplarily shows a controller structure according to the invention.

[0035] Fig. 1shows a schematic representation of a wind turbine according to the invention. The wind turbine 100 has a tower 102 and a nacelle 104 on the tower 102. An aerodynamic rotor 106 with three rotor blades 108 and a spinner 110 is provided on the nacelle 104. During operation of the wind turbine, the aerodynamic rotor 106 is set in rotation by the wind and thus also rotates an electrodynamic rotor or rotor of a generator, which is directly or indirectly coupled to the aerodynamic rotor 106. The electrical generator is arranged in the nacelle 104 and generates electrical energy. The pitch angles of the rotor blades 108 can be changed by pitch motors at the rotor blade roots of the respective rotor blades 108.

[0036] Fig. 3 shows schematically and exemplarily a controller structure 300 according to the invention for a wind turbine 100, as can be seen for example in Fig. 1The controller structure 300 is designed as a cascade control and has an outer control loop 310 and an inner control loop 350. The controller structure 300 regulates a speed in the wind turbine to a setpoint N Target . For this purpose, the outer control loop 310 compares the actual speed N Is with the target speed to be controlled N Target and generates a setpoint 340 of the rotor acceleration power P Acceleration_Target by means of a signal from a P-controller 320 limited by a limiter 330.

[0037] The inner control circuit 350 now regulates the rotor acceleration power P Acceleration and therefore attempts to position the rotor blades of the wind turbine 100 in such a way that the rotor 106 accelerates as little as possible. For this purpose, a calculation unit 380, for example based on the temporal change in the rotor speed dN Is / dt by a calculation unit 380 an actual acceleration power P Acceleration The difference between the target value 340 of the acceleration power P Acceleration_Target and the determined actual value P Acceleration is converted into a settable pitch rate or a settable blade angle of the rotor blades 108 using a P controller 360. A limiter 370 limits the settable pitch rate or pitch angle, which is then transferred to the control of the wind turbine 100 as a setpoint 390.

[0038] In this example, the calculation unit 380 uses known physical relationships between the moment of inertia known for the rotor J , a torque M and speed or derived angular velocity ω back to calculate the actual acceleration power from the change in speed P Acceleration to calculate.

[0039] Instead of the rotor acceleration power, as described in the exemplary embodiment, it is also possible to use the total aerodynamic power absorbed by the rotor, i.e., in addition to the power absorbed by the generator. An advantage of the rotor acceleration power is that in many cases, this variable is usually already available for wind estimators used in the control of wind turbines 100, meaning that further adaptation of the control of the wind turbine 100 is not necessary. It is therefore sufficient to simply replace the known speed controller with a controller structure 300 according to the invention. Wind estimators are known, for example, from the German patent publication DE 10 2017 105 165 A1.

[0040] As an alternative to power, the controller structure 300 presented as an example can also be implemented with torques or time-derived speeds. These solutions are identical except that the current speed is included in the acceleration power. However, it is well known how power is converted into torques and vice versa.

[0041] The inner control loop 350, taken on its own, would lead to significant speed errors over time, so that the outer control loop 310, which reacts significantly slower and more sluggishly, generates a setpoint for the acceleration power that may deviate from 0 kW. For example, if an overspeed situation exists, meaning that the actual speed N Is greater than the target speed N Target the setpoint 340 would be -200 kW. The inner control loop 350 would then provide an approximate rotor acceleration power P Accelerationof -200 kW, so that the rotor 106 reduces speed as a result.

[0042] Limiting the output of the speed controller by limiters 330 and 370 allows the maximum acceleration power to be limited, which also has a load-reducing effect.

[0043] The most advantageous is the Fig. 3 The schematically shown controller structure 300 can be supplemented by a pilot control arranged parallel to the inner control loop 350. The pilot control can, for example, pre-control in response to impending gusts and thus actively intervene in the pitch angle control in addition to the control. This can be particularly effective in avoiding extreme loads, such as those resulting from strong gusts.

[0044] In summary, the controller structure according to the invention therefore means a controller structure 300 for controlling the speed to a speed setpoint N TargetThe inner control loop 350 receives the aerodynamic power absorbed by the rotor 106 or the acceleration power, or simply the rotor acceleration, as the controlled variable, with the pitch rate or, alternatively, a desired rotor blade angle serving as the manipulated variable. The outer control loop 310 controls the rotor speed as the controlled variable. N , whereby a setpoint value of the aerodynamic power, the acceleration power or the setpoint rotor acceleration is generated as a control variable for the inner control loop 350.

Claims

1. A controller structure (300) for a wind turbine (100) having an aerodynamic rotor (106) with at least one rotor blade (108), wherein the controller structure (300) is designed to control a rotation speed (n) of the rotor (106) of the wind turbine (100), wherein the controller structure (300) is designed as a cascade control arrangement and has an outer control loop (310) and an inner control loop (350), wherein the inner control loop (350) receives an input signal (340) which comprises a change in the rotation speed, an acceleration of the rotation speed, a function of the change in the rotation speed and / or a function of the acceleration of the rotation speed, characterized in that the input signal of the inner control loop (350) comprises a rotor acceleration power or a rotor acceleration torque, wherein the rotor acceleration power or the rotor acceleration torque describes the portion of a power or torque received by the rotor (106) of the wind turbine (100) that is converted into an acceleration of the rotor (106).

2. The controller structure (300) as claimed in claim 1, wherein a controlled variable of the outer control loop (310) is provided as reference variable of the inner control loop (350), wherein the outer control loop (310) is in particular designed to limit a target value of the inner control loop, in particular the change in the rotation speed, the acceleration of the rotation speed, the function of the change in the rotation speed and / or the function of the acceleration of the rotation speed.

3. The controller structure (300) as claimed in one of the preceding claims, wherein the input signal of the inner control loop (350) comprises an aerodynamic power received by the rotor (106), wherein the aerodynamic power received by the rotor (106) comprises a sum of the rotor acceleration power and at least one power received by a further component of the wind turbine (100), in particular a generator power of a generator of the wind turbine (100).

4. The controller structure (300) as claimed in one of the preceding claims, wherein the outer control loop (310) determines a deviation of an actual rotation speed of the rotor (106) from a target rotation speed of the rotor (106) as a system deviation.

5. The controller structure (300) as claimed in one of the preceding claims, wherein the outer control loop (310) generates a target value (340) of a power or of a torque as manipulated variable, wherein the target value (340) of the power is preferentially limited upward and downward, wherein in particular the target value (340) of the power is asymmetrically limited upward and downward.

6. The controller structure (300) as claimed in claim 5, wherein the power comprises a rotor acceleration power, wherein the rotor acceleration power is limited to a rated power of the wind turbine (100), in particular to at most 20% of the rated power of the wind turbine (100).

7. The controller structure (300) as claimed in one of claims 5 or 6, wherein the power comprises an aerodynamic rotor power, wherein the aerodynamic rotor power is limited to twice a rated power of the wind turbine (100), in particular to at most 120% of the rated power of the wind turbine (100).

8. The controller structure (300) as claimed in one of the preceding claims, wherein the inner control loop (350) generates, as manipulated variable, a pitch angle or a rate of change in a pitch angle of at least one of the rotor blades (108) of the rotor (106), wherein the target value (340) for the rate of change in the pitch angle is preferentially limited, in particular to a value of between -18° / s and 18° / s and particularly preferably to a value of between -5° / s and +5° / s.

9. The controller structure (300) as claimed in one of the preceding claims, wherein the outer control loop (310) and / or the inner control loop (350) have / has a P controller (320) and / or a PI controller.

10. The controller structure (300) as claimed in one of the preceding claims, wherein the controller structure (300) further has a calculation component which is designed to determine a rotor acceleration power from a change in a measured actual rotation speed of the wind turbine (100) using the rotor inertia.

11. The controller structure (300) as claimed in one of the preceding claims, wherein the controller structure (300) further has a pilot control arrangement for pilot control of a pitch angle of at least one rotor blade (108), which pilot control arrangement is designed to prespecify, parallel to the inner control loop (350), a pitch angle and / or a rate of change in the pitch angle.

12. A method for operating a wind turbine (100) having an aerodynamic rotor (106) with at least one rotor blade (108), wherein the method is designed to control a rotation speed of the rotor (106) of the wind turbine (100), wherein the method is designed as a cascade control arrangement and has an outer control loop (310) and an inner control loop (350), wherein the method comprises the following step: acquiring, by the inner control loop (350), an input signal which comprises a change in the rotation speed, an acceleration of the rotation speed, a function of the change in the rotation speed and / or a function of the acceleration of the rotation speed, characterized in that the input signal of the inner control loop (350) comprises a rotor acceleration power or a rotor acceleration torque, wherein the rotor acceleration power or the rotor acceleration torque describes the portion of a power or torque received by the rotor (106) of the wind turbine (100) that is converted into an acceleration of the rotor (106).

13. A wind turbine (100) having a controller structure (300) as claimed in one of claims 1 to 11.

14. A wind farm having a plurality of wind turbines (100) as claimed in claim 13.