WO2012066107A2

WO2012066107A2 - Method for determining operational states of a wind turbine

Info

Publication number: WO2012066107A2
Application number: PCT/EP2011/070411
Authority: WO
Inventors: Michael Schulz; Ingo Ibendorf
Original assignee: Suzlon Energy Gmbh
Priority date: 2010-11-17
Filing date: 2011-11-17
Publication date: 2012-05-24
Also published as: DE102011086608A1; WO2012066107A3; WO2012066107A9; WO2012066107A4

Abstract

The invention relates to a method for determining the rotational speed of the rotor of a wind turbine and/or for monitoring the state of a rotor blade of a wind turbine, comprising the following method steps: measuring the current of at least one blade adjustment motor of a wind turbine over a predetermined period of time, characterized in that the rotational speed of the rotor is determined by ascertaining the period of oscillation of the motor current, and the rotor position is determined by way of zero point evaluation and gradient evaluation, and/or the state of the rotor blade is determined with the aid of a time or frequency analysis of the motor current of at least one blade adjustment motor.

Description

METHOD FOR DETERMINING OPERATING CONDITIONS OF A WIND TURBINE

The invention relates to an apparatus and a method for determining and monitoring operating states of a rotor of a wind turbine or of a single rotor blade of a wind turbine.

The term operating states, which are determined or monitored according to the invention, on the one hand to understand important operating parameters, such as the rotor speed or the wind speed and the detection of dangerous gusts of wind. The term operating states in the context of the invention, however, also other states to understand, such as the static integrity of the rotor blades, the presence of an imbalance relative to the rotor blades, the presence of icing on a rotor blade or the detection of a sheet bearing with increased friction due a clamping leaf bearing.

In order to determine and monitor such operating conditions, it is known from the prior art to provide a plurality of sensors.

For example, in accordance with the current state of the art, rotor speed detection in a wind turbine is sensor-assisted on the slow shaft (transmission input shaft). The signal evaluation takes place by means of a transmitter relay (eg FR1) or SPS (turbine control) and is used for rotor overspeed detection. A disadvantage of this method is that the detection and evaluation of the rotor speed must be outside the rotor. With a simultaneous loss of Communication with the pitch system and the overspeed that exists may cause the system to stop responding to the system's hazardous condition.

In order to determine and monitor the static integrity of the rotor blades, according to the prior art, sensors, such as acceleration sensors, are necessary to detect damage, cracks, etc. in the rotor blades.

Also, the imbalance or the presence of ice on the rotor blades must be determined according to the prior art with certain sensors.

Likewise, according to the prior art, the variation of flow conditions of the individual rotor blades is recorded with certain sensors in order, if necessary, to generate a better flow behavior via the adjustment of the rotor blades.

A disadvantage of the prior art solutions is that a plurality of sensors is necessary to detect the individual operating conditions. Also, the signals of these sensors usually have to be forwarded to a central control unit, which is often arranged in the nacelle of a wind turbine. This can lead to transmission errors due to the signal transmission between fixed and moving parts.

The aim of the invention is therefore to reduce the mentioned problems of the prior art and at the same time to reduce the costs for the determination and monitoring of the operating conditions. According to the invention, this object is achieved by determining and monitoring the operating states with the aid of an evaluation and analysis of the motor current of one or more pitch-adjusting motors.

The blade displacement motors of wind turbines according to the prior art serve on the one hand to adjust the blade angle so that the most effective angle of attack is driven in the operating state. On the other hand, the blade pitch motors are used also to keep the blade angle set at a certain time constant, so that the rotor blades do not turn unintentionally in the direction of the flag position.

The drive described here can be implemented with AC motors with inverters and also with DC motors and converters. Surprisingly, it has been shown that the blade moment is dependent on the angle of rotation of the rotor blade. The leaf moment is the moment acting on each rotor blade and causing a change in the blade pitch without a torque applied by the blade timing motor in the opposite direction. Accordingly, the moment of the blade adjustment motor and thus also the motor current are dependent on the angle of rotation. This has the consequence that, in accordance with the periodically changing to the angle of rotation leaf torque and the necessary holding torque by the Blattverstellmotor and thus the motor current changes periodically and largely proportional to the rotation angle.

The method according to the invention is therefore characterized in that operating states, such as the rotor speed, are determined or monitored by means of an analysis of the varying motor current of one or more blade pitch motors. The device according to the invention is characterized in that a control unit connected to at least one pitch motor is designed to determine an operating state, such as the rotor speed, with the aid of the motor current of at least one pitch motor.

The crucial point of this invention is the direct detection of important operating conditions - such as rotor speed or rotor position by means of the motor current of at least one pitch motor, preferably directly in the rotor. The advantage here is the achievable precision of the measurement in conjunction with the possible very short reaction time. There are no additional encoders required for the determination of the rotor speed or the rotor position or the other operating states, since the currents of the Blade adjustment motors in each wind turbine are used directly for evaluation. The evaluation is preferably carried out directly in the rotor.

According to one embodiment of the method according to the invention, the period of the motor current and thus the rotor speed are determined by means of a peak detecting method. The rotor speed may then be used directly to control the wind turbine according to one embodiment. However, numerous other methods for determining the rotor speed from the one or more motor currents of the pitch motors are possible and provided according to further embodiments, such as the period measurement, the frequency count, the zero point evaluation, etc.

For the rotor position determination, the zero point detection is preferably combined with the gradient evaluation. According to a further embodiment, the period is determined by the determination of the saddle points in the vibration of the motor current. According to a further embodiment, the zero crossing of the motor current is used to determine the period duration. According to a preferred embodiment, the curves of at least two, and more preferably the curves of three pitch motors, are used together to determine the rotor speed.

The use of multiple curves to determine the period and thus the rotor speed according to the invention allows a safer determination of the speed, since the curves of the individual blade timing motor currents are not always completely harmonious and therefore the determination of the speed with the help of only one blade pitch motor may lead to false results could.

According to a variant, the currents of the individual motors are added (or subtracted) and from the resulting curve, the rotor speed is determined. Also, individual current waveforms can be compared in terms of their spectra or other functions for Comparison of the individual current curves can be applied. Other methods by means of phase shift and mean calculation are part of the invention.

It is also conceivable that comparison current profiles or comparison spectra are stored in a memory means, which are used for the evaluation or analysis of the real current waveforms or their spectra.

According to a particularly preferred embodiment of the method according to the invention, a critical change in the rotor speed of the wind turbine can already be determined within a period, in particular within a half-period. For this purpose, first the currents of the preferred three blade pitch motors are measured. These are then subtracted over time according to the formula A _ges = A ₁ (- A ₂ (- A ₃ (In this context, an addition would work the same way because the subtraction of known measures is the inverse of the addition.) In a next step the derivative of this function A (ges) formed by the currents of the three pitch motors after the time according to the formula

From a comparison of the value of this derivative function with the value of the derivative function of a half-period before, which was previously stored in a data memory and read out again, a critical change in the rotor speed can be detected particularly quickly. Thereby, for example, a recognition of a Liberdrehzahl by a control unit, which is arranged directly in a rotor of a wind turbine, are made and used directly for controlling the blade pitch motors. Possible measurement errors and longer measurement times, which are associated with the detection of Liberdrehzahlen in the main control unit of a wind turbine, for example by the need for the transmission of sensor signals via sliding contacts, are thus avoided. From the flow of a respective blade displacement motor is monitored according to a further embodiment of the invention, whether a respective rotor blade has cracks or fractures. It has been found that cracks or breaks in the rotor blades cause the periodic course of the motor current to be superimposed by vibrations occurring during the opening and closing of a crack. These vibrations have a characteristic curvature or a characteristic frequency spectrum and can be analyzed from the motor current. Imbalance, icing on the rotor blades and occurring flow changes (for example, by the entry of a rotor blade in a wind shadow induced by the tower) lead to characteristic vibrations, which indicate according to the invention via an analysis of the motor current of the pitch motor to a specific operating condition. Whether imbalance, icing or cracks - each of these operating states shapes the periodic course of the motor currents of the blade timing motors in a very specific way. The various operating states also characteristically occur in regions of particular angles of rotation, or tend to repeat themselves periodically in a characteristic pattern. At the same time, the strength of the changes produced by the different operating states of the motor currents or currents is characteristic, and thus they can be determined by means of defined threshold values. In the case of a blade displacement motor, when maximum currents occur which vary from the average of the maximum currents of the other two pitch motors by a predetermined factor, an embodiment indicates that a faulty operating condition exists. Preferably, in a first step, the current of a first pitch motor [(of a first rotor blade) is measured

Current characteristic is broken down by means of an FFT the frequency spectrum of the current. In a next step, this frequency spectrum with that in a data memory stored frequency spectrum of the same rotor blade, which was previously recorded during a known intact and unvereisen state before. If in each case the difference of individual frequencies between the currently determined frequency spectrum and the recorded frequency spectrum is above a predetermined threshold value, it is assumed that cracking or icing of the examined rotor blade is present and appropriate measures, such as shutting down the system and / or sending a Alarm signal is triggered.

According to another embodiment, the frequency spectrum of the pitch motor of the rotor blade to be examined is compared with the frequency spectrums of the currents of the blade pitch motors of the other two rotor blades. If one or more frequencies of the spectrum are out of the way of the other two rotor blades and exceeds a limit value, it is possible to conclude the presence of cracks or fractures in a rotor blade.

In order to determine bearing problems, the current of a pitch motor is integrated over a predetermined period of time according to a further embodiment and that in such a time interval in which we adjusted the angle of attack of the rotor blade. If the value of this integral is above the integral values of the other two pitch motors plus a predetermined tolerance value in the same time period, then a damaged blade bearing can be assumed and an alarm signal is preferably triggered or forwarded.

According to a further embodiment for determining bearing problems, in a first step the current of a pitch motor of a rotor blade ^ (t) is measured over the course of time. Over this time interval, the integral is then formed. In a next step, this integral is compared with a value stored in a database, which corresponds to the integral of the motor current of the same rotor blade over the same time interval, and was detected during a period in which the bearing was known to be fully functional. If the difference between these two integrals lies above a predetermined limit or tolerance value, it is assumed that the bearing is defective and may require repair or replacement. For this reason, when the said limit value is exceeded, preferably damage-limiting actions such as shutting down the wind turbine are triggered and / or an alarm signal is triggered. The device according to the invention comprises a control unit, which is connected to one, preferably to two, and particularly preferably to three pitch motors, and which is designed to detect and monitor the presence of specific operating states using the method steps described above. In this case, the control unit is preferably arranged in the hub or in the rotor). According to a further embodiment, however, the control unit is arranged in the nacelle. According to a further embodiment, said control unit, which is designed to determine operating conditions by analyzing the motor current of at least one pitch motor, is part of a safety system which, when an undesired operating condition is detected, acts on the blade pitch motors and / or on a separate pitch system the wind turbine is returned to a safe operating condition or braked according to another embodiment. According to a further alternative embodiment of the invention, the control unit is arranged in the hub and not or only part of a safety system, but directly designed to act on the blade displacement motors such that the wind turbine can be maintained in the operating state at a desired optimum operating point. In this case, for example, a rotor position-optimized pitch control of the leaves takes place. According to a further embodiment of the invention, the control unit is also connected to a database, in which the curves obtained during a test run of the individual blade pitch motors are stored at different speeds. This makes it possible for the control unit to conclude by comparing the currently measured current waveforms with the stored values to a specific operating state or to determine a faulty operating state. In the Database can also be characteristic curves of other systems stored.

figure description

FIG. 1 shows the engine currents of the three blade pitch motors of a wind turbine over time. In the first three curves Α ^, Α ^ and A _g it) are the

Currents of the three pitch motors are shown in amperes over time. In the fourth curve, the combination, in this case the difference, of the three overlying curves is shown. According to the embodiment shown here, the period duration and thus the rotational speed of the rotor is determined from the curve of this, resulting from the 3 engine currents curve.

FIG. 2 shows the method steps performed by the control unit for determining the position of a rotor blade of a wind turbine:

First, the currents of the three blade pitch motors of a wind turbine

A _j OA _j Ct) and A ₃ (t). These are subtracted over time according to the formula (A ₁ (t) -A ₂ (t) -A ₃ (t)). In a next step, the derivative of this function, formed from the currents of the three pitch motors, is determined according to time

Formula (A ₁ (t) - A ₂ (t) -A ₃ (t)) derived. In addition, from the through the streams of the three dt

Blade adjustment motors formed function which determines zero points. By means of the combination between zero points of the formed function and the information as to whether the derivative of the said function after time at a zero point is greater or less than zero, one can exactly determine the position of a single sheet, namely either the sheet is moving at that moment past the tower or pointing vertically upwards, depending on whether the derivative is greater or less than 0 at this point. The phase of the current of the blade pitch motor for the first rotor blade corresponds to the phase of the function A _ges (t) = (A ₁ (t) -A ₂ (t) -A ₃ (t)) formed from all three pitch motors. so that no phase shift is to be considered in relation to the position determination of the first rotor blade. However, the installation direction of the blade pitch motors and thus the current flow direction of the blade pitch motors must be taken into account. FIG. 3 shows a first method sequence for determining a state of a rotational speed, which leads to the shutdown of a wind turbine. In the process, the currents of the three blade pitch motors of a wind turbine are first of all again

A _l (t), A ₂ (t) and A ₃ (t) are measured. In the next two steps, again, the currents are subtracted over time according to the formula [A _l {t) - A ₂ {t) - A ^ it)), and the derivative thereof is formed from the currents of the three pitch motors

Function according to the time according to the formula - (A _l (t) - A ₂ (t) - A ₃ (t)) derived. If the dt

As the speed of a wind turbine increases, the value of the derivative of the function formed from the currents of the individual pitch motors increases in absolute value, determined during a half-period. For this reason, a Liberdrehzahl is considered to be established if ^■ ^ - (A _l (t) _-A ₂ (t) _-A ₃ (t)) _{miix is} above a specified threshold at normal _speed plus tolerance.

FIG. 4 shows a second method sequence for determining a state of an overspeed, which leads to the shutdown of a wind turbine. This process sequence shown in FIG. 4 has the advantage that an overspeed is possible even before the maximum value of the derivative of the function formed by the currents of the blade displacement motors has been reached. In this case, the currents of the pitch motors are measured and the zero crossings of the function formed by the individual currents are determined and provided with a pointer. The derivatives of the function formed by the currents of the blade pitch motors, which are formed at approximately 100 points within one half-cycle, are buffered in a memory. In a next half-period, the derivatives are again formed at about 100 points and with the one Half-period ago values compared in terms of amount. If it is ascertained in this case that a plurality of derivation values formed, for example, 5 consecutively formed derivative values are greater than the derivative values previously determined in each case for a half period and, in addition, from the measured half-period time it appears that the rotational speed lies at the upper end of the rotational speed tolerance range, then a rotational speed is considered determined and the wind turbine is shut down.

FIG. 5 shows a method sequence in which the condition of the bearings, that is to say the occurrence of bearing problems, is monitored. In each case, the integrals of the individual pitch control motors are measured over a period of time by performing at least one pitch adjustment. Preferably, however, a larger period is selected. The integral values of the individual currents of the pitch motors are compared with the average of the integrals of the other two pitch motors. If the value of an integral of a pitch servo motor is above the average value of the integral of the other two pitch motors plus a tolerance value, then bearing damage is assumed.

Claims

claims

1. A method for determining important operating conditions of a wind turbine, such as the speed of the rotor of a wind turbine or the static integrity of a rotor blade, with the method steps:

Measuring the current of at least one blade displacement motor of a wind turbine for a predetermined period of time

characterized in that the determination of the operating conditions, by means of an analysis of the current-time function of the motor current, such as the calculation of the period duration, at least one pitch servo motor or by means of an analysis of the frequency spectrum of the motor current takes place in a predetermined period.

2. A method for determining important operating conditions of a wind turbine, according to claim 1, characterized in that the rotational speed of the rotor by means of a function formed from the sum or difference of the current-time functions of at least two pitch motors of a wind turbine is determined.

3. A method for determining important operating conditions of a wind turbine, according to claim 2, characterized in that a state of Liberdrehzahl the rotor by means of the derivative of a function formed from the sum or difference of the current-time functions of at least two pitch motors of a wind turbine is determined.

4. A method for determining important operating conditions of a wind turbine, according to claim 1, characterized in that the position of a rotor blade by means of the derivative of a function formed from the sum or difference of the current-time functions of at least two blade pitch motors of a wind turbine in conjunction with the determined zero crossings or Saddle points of this function is determined.

5. A method for determining important Betnebszustande a wind turbine, according to claim 1, characterized in that the detection of cracks or icing of a rotor blade made by comparing a FFT spectral analysis of the motor current in a predetermined period with a stored in a database reference spectral pattern of the same rotor blade becomes.

6. A method for determining important Betnebszustande a wind turbine, according to claim 1, characterized in that the detection of cracks or icing of a rotor blade by comparing a FFT spectral analysis of the motor current in a given period of time with a FFT spectral analysis of the motor current of at least one further rotor blade in a corresponding Period is made.

7. A device for determining important operating conditions of a wind turbine and / or for monitoring the operating state of a rotor blade of a wind turbine with a control unit, characterized in that the control unit is connected to at least one pitch motor and is adapted to, using the method according to claim 1, the operating conditions to monitor at least one rotor blade.

8. A device for determining important operating conditions of a wind turbine and / or for monitoring the operating state of a rotor blade of a wind turbine according to claim 7, characterized in that the control unit is arranged in the rotor of the wind turbine.

9. A device for determining important operating conditions of a wind turbine and / or for monitoring the operating state of a rotor blade of a wind turbine according to claim 8, characterized in that the operating states determined in the control unit are used directly for controlling the blade pitch motors.