Method for estimating state of health of pitch energy storage unit of wind turbine and pitch control system

Abstract

A method for estimating a state of health of a pitch energy storage unit of a wind turbine and a pitch control system of a wind turbine are provided. The method comprises: providing an equivalent circuit model (ECM) of the pitch energy storage unit, the ECM comprising at least at least one electrical energy storage element and an equivalent series resistor connected between two power supply terminals; repeatedly sampling voltages and corresponding currents at the two power supply terminals; determining at least one voltage change and at least one current change for the plurality of voltage samples and corresponding current samples; performing an optimization process based at least on the ECM, the plurality of voltage samples, the determined voltage variation, and the determined current variation to obtain an updated resistance of the equivalent series resistor and at least one updated model parameter of the at least one electrical energy storage element; and estimating at least one health state parameter of the pitch energy storage unit by comparing at least one of the updated resistance and the at least one updated model parameter to a threshold.

Description

Technical Field

[0001] The present invention relates to a health status of a pitch energy storage unit of a wind turbine, a method for charging a pitch energy storage unit of a wind turbine, and a pitch control system of a wind turbine. Background Art

[0002] Wind turbines are well known in the prior art and are used to convert wind energy into electrical energy. Among other things, the wind turbine may include an energy storage unit for providing electrical energy to all or some parts of the wind turbine, for example in the event that the wind turbine does not generate sufficient energy and is at least temporarily disconnected from an external energy source such as a power grid or during situations such as a power grid fault ride-through (FRT).

[0003] In particular, the wind turbine may include a so-called pitch energy storage unit which stores sufficient electrical energy to control the pitch angle of the rotor blades of the wind turbine. For example, in case a previously deactivated wind turbine needs to be activated or started, the pitch drive may change the pitch angle of the rotor blades to start the wind turbine. Other operations powered by the pitch energy storage unit may include (self)test functions of the wind turbine.

[0004] The operating phases in which power is provided by the pitch energy storage unit are infrequent and relatively short compared to normal operating phases of the wind turbine, in which the wind turbine provides power to the grid or is deactivated. However, a reliable supply of power is crucial in such operating phases, since this enables safe activation and deactivation of the wind turbine in particular in special situations such as grid failures and / or extreme weather situations such as gusty winds.

[0005] Like many other components, the performance of the pitch energy storage unit deteriorates over time. For example, rechargeable batteries used as energy storage for the pitch energy storage unit have a limited lifespan in terms of years, charging cycles, etc. However, it is challenging to detect defective storage devices well in advance, and additional hardware, computing power, effort and cost are usually required to monitor them. Therefore, in practice, the entire pitch energy storage unit or its internal energy storage components are usually replaced at regular maintenance intervals to avoid unexpected shutdowns of the wind turbine and / or damage to the wind turbine due to insufficient energy stored in the pitch energy storage unit. Replacing the pitch energy storage unit or its internal energy storage components is expensive, resource-intensive and can be dangerous. In addition, it usually requires the wind turbine to be deactivated or stopped for maintenance, which therefore reduces the amount of energy provided to the grid.

[0006] Therefore, there is a need to monitor the health or remaining life of the pitch energy storage unit and / or detect defective storage components included in the pitch energy storage unit at an early stage to avoid unexpected shutdown of the wind turbine and / or damage to the wind turbine, and at the same time prevent unnecessary maintenance and / or replacement of the pitch energy storage unit. Summary of the invention

[0007] According to a first aspect of the present disclosure, there is provided a method for estimating a health state of a pitch energy storage unit of a wind turbine. The method comprises:

[0008] - providing an equivalent circuit model ECM of the pitch energy storage unit, the ECM comprising at least at least one electrical energy storage element connected between two power supply terminals and an equivalent series resistor;

[0009] - The voltage u and the corresponding current i at the two power terminals m Repeated sampling;

[0010] - determining at least one voltage change and at least one current change for a plurality of voltage samples and corresponding current samples;

[0011] - performing an optimization process based at least on the ECM, the plurality of voltage samples, the plurality of current samples, the determined voltage change and the determined current change to obtain an updated resistance R of the equivalent series resistor i and at least one updated model parameter of at least one electrical energy storage element; and

[0012] - By replacing the updated resistor R i At least one of the updated at least one model parameter is compared with at least one threshold value to estimate at least one health state parameter of the pitch energy storage unit.

[0013] In particular, the inventors have found that the health state of a pitch energy storage unit can be reliably estimated based on providing an equivalent circuit model (ECM) and incremental updates of the ECM parameters of the pitch energy storage unit. At the same time, the disclosed method is computationally efficient and can be implemented, for example, using existing controllers of a wind turbine, such as controllers of a pitch converter. Thus, health state monitoring and predictive maintenance can be achieved with no or very limited additional effort.

[0014] In contrast to known methods, the disclosed method does not require the provision of additional components such as dedicated sensors or measuring devices, does not require disconnecting the pitch energy storage unit, for example, to determine the open circuit voltage or resistance of the pitch energy storage unit, or to perform a complete discharge and / or charge cycle of the energy storage element contained therein. Instead, the health status of the pitch energy storage unit can be determined in situ while the turbine is operating, and preferably continuously, in order to minimize and schedule maintenance as needed, while preventing unplanned downtime.

[0015] In at least one implementation, the optimization process is based on a predetermined number of sample tuples, each sample tuple comprising a current voltage sample, a corresponding time derivative du / dt of the voltage u, a current current sample i m And the current i m The corresponding time derivative di m The optimization process is performed when a predetermined number of sample tuples have been stored in the buffer storage device in order to ensure sufficient data for successful optimization.

[0016] In at least one implementation, the method further comprises: determining whether the current sample tuple satisfies at least one predetermined filtering criterion, in particular, determining whether the current sample tuple is different from all sample tuples contained in the buffer storage device. If at least one predetermined filtering criterion is satisfied, the current sample tuple is added to the buffer storage device. Otherwise, the current sample tuple is discarded. By filtering out inappropriate samples, such as duplicate samples, the quality of the optimization can be improved.

[0017] In at least one implementation of the method, the optimization process is performed multiple times, and the method further comprises: selecting a starting value for a set of optimization parameters optimized by the optimization process; determining at least one quality parameter associated with an updated value of the set of optimization parameters obtained after performing the optimization process starting from the starting value, such as a residual sum of squares RSS nev ; and if at least one quality parameter RSS associated with the optimization parameter set nev If at least one quality condition is met, an updated resistance of the equivalent series resistor and an updated at least one model parameter of the at least one electrical energy storage element are calculated, otherwise the previously calculated resistance of the equivalent series resistor and the at least one model parameter of the at least one electrical energy storage element are kept. By using an iterative optimization method that minimizes the quality parameters, the calculation method can be reduced in each round. In particular, the parameters of the ECM are only updated when the optimization step has actually obtained a better approximation of the optimization parameters.

[0018] In at least one implementation, the optimization process is performed using a gradient optimizer, wherein the gradient optimizer performs up to k max optimization steps, where k max≥1; and the gradient optimizer minimizes the residual sum of squares (RSS). The use of the gradient optimizer is computationally efficient and approximates the modeling parameters particularly quickly.

[0019] In at least one implementation, the step of estimating the health state of the pitch energy storage unit comprises: comparing at least one updated parameter of at least one electrical energy storage element with a nominal parameter value of at least one electrical energy storage element, in particular, with a predetermined multiple of the nominal parameter value; and / or comparing the updated resistance R i The comparison is made with a nominal resistance value of the equivalent series resistor, in particular with a predetermined multiple of the nominal resistance. Note that the term "multiple" in this context may also refer to a fractional multiple, i.e. the case where the corresponding threshold value is less than a given nominal value. By observing updated characteristic parameters such as capacity and / or series resistance of the pitch energy storage unit and comparing them with reference values, e.g. taken from a data sheet, its health state can be well estimated.

[0020] In at least one implementation, the pitch energy storage unit includes at least one capacitor for pitch energy storage, in particular a supercapacitor, at least one energy storage element of the ECM is an equivalent capacitor, and the updated parameter corresponds to an updated capacitance C of the equivalent capacitor. Capacitor-based pitch energy storage units have many advantages, including a greater number of charge cycles compared to rechargeable batteries, and can be modeled based on their capacity and series resistance using the disclosed method.

[0021] In at least one implementation, the method further includes: if the health status indicates that the pitch energy storage unit is at or near its beginning of life BoL, charging the capacitor to a first charging voltage sufficient to provide a predetermined amount of electrical power and / or energy. If the health status indicates that the pitch energy storage unit is at or near its end of life EoL, charging the capacitor to a second charging voltage sufficient to provide a predetermined amount of electrical power and / or energy, wherein the second charging voltage exceeds the first charging voltage. This adaptive charging model based on the current health status will extend the service life of the capacitor.

[0022] In at least one implementation, the health state indicates an estimated capacitance C of the capacitor, and the charging voltage of the capacitor increases from a first charging voltage to a second charging voltage based on the estimated capacitance C, and in particular increases from the first charging voltage to the second charging voltage in an inversely proportional ratio. Such an approach ensures an optimal charging voltage in all cases.

[0023] According to a second aspect of the present disclosure, a pitch control system for a wind turbine is disclosed. The wind turbine comprises an energy storage unit and a converter circuit, in particular a pitch energy storage unit and a pitch converter. The energy storage unit comprises at least one energy storage device and has at least two power terminals for receiving or providing electrical energy. The converter circuit is connected to the energy storage unit via at least two power terminals to selectively charge or discharge at least one energy storage device of the energy storage unit. The pitch control system also comprises at least one controller, in particular a controller of the converter circuit, at least one controller being configured to implement the method according to the first aspect or any implementation thereof. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Further advantages, features and further developments are explained by the following exemplary embodiments described in conjunction with the accompanying drawings. Identical or similar elements, or elements that act in the same way, are provided with the same reference numerals in the drawings, in which:

[0025] Figure 1 A schematic representation of a wind turbine is shown.

[0026] Figure 2 A schematic representation of a pitch control system is shown.

[0027] FIG. 3A to FIG. 3C An exemplary equivalent circuit model of an energy storage unit is shown.

[0028] Figure 4 The steps of a method for determining the state of health of an energy storage unit are shown.

[0029] Figure 5 Shown is a Figure 3A An equivalent circuit model is used to estimate the health state of a pitch energy storage unit in one cycle of the method.

[0030] Figure 6 shows the estimated Figure 5 The health status method determines the relevant parameter values.

[0031] Figure 7 A flow chart of an adaptive charging method is shown.

[0032] Figure 8 The effect of temperature on the capacitance and series resistance of a capacitor is shown. DETAILED DESCRIPTION

[0033] Figure 1A schematic diagram of a wind turbine 100 is shown that includes a tower 102. The tower 102 is fixed to the ground by a foundation 104. A nacelle 106 is rotatably mounted at one end of the tower 102 opposite the ground. For example, the nacelle 106 includes a generator coupled to a rotor 108 via a rotor shaft (not shown). The rotor 108 includes one or more (wind turbine) rotor blades 110 that are movably arranged on a rotor hub 112.

[0034] During operation, the rotor 108 is set into rotation by airflow (eg, wind). The rotational motion is transmitted to the generator via the rotor shaft with or without a gearbox. The generator converts the mechanical energy of the rotor 108 into electrical energy.

[0035] To control the rotational speed of the rotor, the rotor blades 110 may be adjusted by rotating the rotor blades 110 along a longitudinal axis. The rotation is performed by a pitch control system including one or more pitch drives.

[0036] Figure 2 A pitch control system 120 is shown in a schematic manner. The pitch control system 120 includes one or more pitch drives 122, a pitch controller 124, a pitch converter 126, and a pitch energy storage unit 128.

[0037] Each pitch drive 122 may include an electric motor (not shown), such as a servo motor, and a transmission system (not shown) for coupling the electric motor to at least one of the rotor blades 110. The pitch drive 122 is controlled by a pitch controller 124. The pitch controller 124 may be a separate component or may be an internal controller of another component. It typically includes or has access to a measurement circuit system for measuring the voltage and current provided by the pitch energy storage unit 128. In addition, it typically controls the charging or discharging current of the pitch energy storage unit 128. In the depicted embodiment, the pitch controller 124 forms part of the pitch converter 126. However, this is not limited by the present disclosure. The electrical energy required for the operation of the pitch drive 122 and the pitch controller 124 is provided by the pitch converter 126.

[0038] In normal operation, the electrical energy required by the pitch control system 120 can be obtained from a generator coupled to the rotor 108. In particular, the electrical energy generated by the generator is supplied and stored in the grid, and the pitch control system 120 can draw power from the grid to operate. However, in the case where the rotor 108 is not moving or the generator does not provide sufficient electrical energy, all or part of the electrical energy for the operation of the pitch control system 120 can be provided by other power sources including the pitch energy storage unit 128. This is important because the pitch control system is also important for braking the rotor 108, for example, in the event of strong winds or an emergency shutdown of the turbine. In this regard, the pitch converter 126 and the pitch energy storage unit 128 effectively provide an uninterruptible power supply (UPS) function so that pitch control can be achieved even in the absence of any wind, or during a grid fault, or during a failure of other components of the wind turbine 100, or during a situation such as a grid fault ride-through (FRT) characterized by low or high grid voltage.

[0039] The pitch converter 126 is also responsible for charging one or more energy storage devices 130 (e.g., rechargeable batteries or capacitors) of the pitch energy storage unit 128. In an embodiment of the present disclosure, capacitors may be classified as double-layer capacitors, ultracapacitors (UC), or supercapacitors (SC) based on their storage capacity and other characteristics. For example, UC or SC are high-capacity capacitors with a higher energy density than conventional electrolytic capacitors and a much greater charge-discharge cycle tolerance than rechargeable batteries. However, for simplicity, the term capacitor is used throughout the specification, and capacitors may be interchangeably referred to as ultracapacitors or supercapacitors.

[0040] Charging is typically performed when sufficient electrical energy is available for charging, for example from a generator or a grid to which wind turbine 100 is connected during normal operating conditions. Preferably, pitch energy storage unit 128 should always store sufficient electrical energy to enable pitch control system 120 to at least brake or stop wind turbine 100 to a standstill under the most adverse conditions. Preferably, it should also hold sufficient energy to restart the wind turbine when normal conditions are restored.

[0041] Due to the uncertainty of such emergency operations, the pitch energy storage unit 128 is used rarely and in an unpredictable manner. However, if it is relied upon, it may need to provide a relatively large amount of electrical power and a corresponding high current for pitch change in a relatively short duration, especially with high torque. Therefore, an energy storage device 130 with a relatively high storage and discharge capacity is used in the pitch energy storage unit 128. In addition, such an energy storage device 130 needs to be replaced before its capacity becomes insufficient to provide the required amount of electrical energy, for example due to thermal stress or electrical stress leading to health deterioration.

[0042] Determining the actual storage capacity and / or instantaneous charge or other characteristics of one or more energy storage devices 130 encapsulated in the pitch energy storage unit 128 is a difficult task. For example, the electrolyte of the energy storage device 130, such as a battery, may be affected by environmental stresses in different ways. In addition, the information available to the pitch controller 124 about the internal state of one or more energy storage devices 130 that make up the pitch energy storage unit 128 may be limited or less reliable. Therefore, in practice, the energy storage devices are typically charged at regular intervals or whenever they have been used using a maximum nominal charging voltage, current, or time, and are replaced at regular intervals (e.g., before their shortest possible service life or when they are near the end of their life).

[0043] According to the present disclosure, an improved method for monitoring the health and charge of a pitch energy storage unit is provided.

[0044] like Figure 2 As shown, the pitch converter 126 is connected to the pitch energy storage unit 128 via at least two terminals 132 and 134 (typically a positive direct current (DC) terminal and a negative direct current (DC) terminal). The voltage between the two terminals 132 and 134 and the current flowing through each of these terminals 132 and 134 provide some information about the charging and discharging characteristics of the energy storage device 130. These parameters can be observed from the outside, for example, using corresponding measurement circuitry of the pitch converter 126. However, this information alone is not sufficient to directly estimate the remaining capacity of the energy storage unit 128.

[0045] To better estimate actual storage capacity, the disclosed system utilizes an equivalent circuit model (ECM) of the energy storage unit 128 . Figure 3A An exemplary ECM 140 is shown for an energy storage unit 128 that includes a plurality of capacitors (sometimes also referred to as supercapacitors or ultracapacitors) as energy storage devices 130. For example, the energy storage unit 128 may include a plurality of capacitors connected in series and / or in parallel to form a plurality of storage cells or capacitor banks. Alternatively, a balancing network having one or more circuit elements may be connected in parallel to balance the power provided by each storage cell.

[0046] despite this, Figure 3A The ECM 140 shown in FIG. 1 includes only a single equivalent capacitor 146, which represents the combined capacitance C of all physical capacitors. In addition, a capacitor having a resistance R is shown. i A single equivalent series resistor 148 and having a resistance R pThe optional equivalent parallel resistor 149 of the energy storage unit 128 simulates the internal resistance and loss of the energy storage unit 128. i Corresponds to the internal resistance of the storage unit, all connections, lines, wires, etc. Equivalent parallel resistance R p Corresponds to the leakage current of the capacitor itself or to the losses caused by other components such as the internal passive balancing network.

[0047] Note that nodes 142 and 144 shown on the left side of ECM 140 correspond to terminals 132 and 134 of energy storage unit 128. The voltage u therebetween and the current i measured through, for example, first terminal 132 m It can be observed from the outside. It is more difficult to obtain model parameters, especially equivalent capacitance C, equivalent series resistance R i And the equivalent parallel resistance R p Similarly, modeled internal voltages and currents such as the voltage u_C across capacitor 146 and the currents i_C and i_p through capacitor 146 and parallel resistor 149, respectively, cannot be observed directly. Although these parameters cannot be observed directly, they can be derived indirectly from ECM 140, as described in further detail below.

[0048] In the disclosed embodiment, the estimator is used to determine at least the capacitance C and the series resistance R based on a plurality of samples of the voltage and current measured at the terminals 132 and 134. i Optionally, the estimator can also be used to determine the parallel resistance R p , as described in further detail below. The estimator uses the optimizer to convert the voltage u and current i of the ECM 140 s The voltage and current measured at the terminals 132 and 134 of the energy storage unit 128 are matched to determine real-time values ​​of parameters such as capacitance and internal resistance. The model parameters of the ECM 140 are adjusted by the optimizer. The difference between the measured and calculated values ​​provides a quality factor that measures the quality of the estimate.

[0049] Note the fact that in the target application, the current i_p representing the leakage current of capacitor 146 and the current through the balancing network may be negligible compared to the total current i. Therefore, when the parallel resistor R p The value of is set to a constant or ignored completely and only the model parameter R i When and C are optimized, the proposed method can be simplified and can be more stable. However, as a more general case, described below Figure 3A Optimization of all three model parameters of the ESM 140.

[0050] It is also possible to build a similar ECM and formulate similar differential equations to solve for voltage parameters (instead of current parameters as indicated in the embodiments described in detail above and below). In this case, consider the measured voltage u determined from the ECM m And calculate the voltage u3.

[0051] Definition and Equation:

[0052] The current i through the measurement node 142 calculated from the ECM 140 s It is represented by the differential equation:

[0053] i s : =C / (1+R i / R p )du / dt-CR i (1+R i / R p ) m / dt+1 / (R p +R i )u (1)

[0054] Among them, C, R i , R p and u have the conventional meanings as described above, dx / dt represents the rate of change or time derivative of the parameter x, which in this case is applied to the measured voltage u and the measured current i m On the other hand, the current measured at the corresponding first terminal 132 is denoted above and below as i m The voltage u between the measurement node 142 and the reference node 144 corresponds to the voltage measured across the two terminals 132 and 134 .

[0055] For each optimization interval, the estimator collects four values, namely, the voltage change rate x1, the current change rate x2, the terminal voltage x3, and the current i measured across the terminals. m The measurement sample consists of:

[0056]

[0057] For example, by comparing two subsequent measurements of the time series of measurements performed by the pitch converter 126 or by any other means from u and i m The measured values ​​are used to calculate the time derivatives du / dt and di m / dt. Then the obtained sample, that is, the four-tuple (x1, x2, x3, i m ) are stored in, for example, a circular buffer of size N.

[0058] To simplify the equations, the following optimization parameters are defined:

[0059]

[0060] Each optimization parameter a1, a2 and a3 can be C, R i and R p Using relations (2) and (3), equation (1) can be simplified to:

[0061] i s =a1x1+a2x2+a3x3

[0062] Therefore, the calculated current i is defined as s，n With the measured current i m，n The error of the nth sample of the difference between

[0063] r n =i s，n -i m，n =[(a1x1 n +a2x2 n +a3x3 n )-i m，n ]

[0064] The residual sum of squares (RSS) of all samples is

[0065]

[0066] Or, in an alternative representation, RSS = || Aa - I m || 2 , where A is a matrix including a subset of the first three entries (x1, x2, x3) of each of the N samples, a is a vector of optimization parameters (a1, a2, a3), and I m is the current i corresponding to the measurement m N vectors with the last entry of each of the N samples.

[0067] The goal of the optimizer is to minimize the RSS by adjusting the optimization parameters a1, a2, and a3. This makes the calculated current i s Approximately the measured current i m According to the optimized parameters a1, a2 and a3, the model parameters C, R of the equivalent circuit 140 can be calculated based on the above equations. i and R p .

[0068] Figure 4 The steps of a method 150 for determining a state of health of an energy storage unit are shown more generally. Note that the method 150 may be performed during normal operation of the wind turbine 100, ie, when the rotor 108 is turning and the generator is providing electrical energy to a grid.

[0069] In method step 152, a suitable ECM is provided. For example, providing an ECM 140 may be used to estimate the current capacitance or health state of an energy storage unit 128 including a plurality of capacitors as energy storage device 130. Alternatively, an ECM based on a different type of energy storage device may be used, such as an ECM including a voltage source and a shunt resistor, which represents an energy storage unit 128 including one or more rechargeable batteries.

[0070] Figure 3B A corresponding first-order ECM 240 is shown for the battery-based energy storage unit 128, and Figure 3C A corresponding n-th order ECM 250 is shown for the battery-based energy storage unit 128. The corresponding equations for the ECM 240 and the ECM 250 can be derived based on similar observations as described in detail above with respect to the ECM 140. In the ECM 240 and the ECM 250, the voltage U(SoC) is a function of the state of charge (SoC) of the battery-based energy storage unit 128.

[0071] In method step 154, initial values ​​are provided for the estimator. For example, known reference values, such as values ​​defined in the specifications of the original equipment manufacturer (OEM), may be provided for the new energy storage unit 128. Alternatively, the initial values ​​may be calculated based on the known physical configuration and technical specifications of the used components taken from corresponding data sheets.

[0072] In method step 156 and method step 158, the sampling means measures the voltage u and the current i across / at the terminals 132 and 134. m Steps 156 and 158 may be performed at regular intervals, such as once every second or every minute, or may be triggered by a specific event, namely, activation of a service routine, detection of a charging or discharging event, or a combination of both.

[0073] As described in detail below, method step 156 and method step 158 may need to be repeatedly performed before the optimization is performed for the first time. In at least some embodiments, steps 156 and 158 are performed throughout operation of wind turbine 100.

[0074] In subsequent method steps 160 and 162, the sampling component calculates the time derivatives du / dt and di respectively relative to the previously taken samples. m / dt. In addition, the sampling component can weight and / or select the samples, as described in further detail below. For example, only samples that meet certain criteria such as predefined measurement quality, proximity to a relevant operating point and / or uniqueness are considered and placed into, for example, a ring buffer.

[0075] When new samples are added in further iterations of method steps 156 to 162 , and in case of a finite data structure such as a ring buffer, the oldest samples may be previously removed or overwritten by the new samples.

[0076] Once a sufficient number of samples are available, such as when the ring buffer is full, the optimizer can start working, as shown in method step 164. The optimizer provides, for example, an equivalent capacitance C of the ECM 140, an equivalent series resistance R i and optionally an equivalent parallel resistance R p The updated values ​​of the model parameters are taken as its output.

[0077] As described in further detail below, the optimizer can be implemented as a gradient optimizer. This helps minimize the computational workload. In each time step, the optimizer only takes a limited number of optimization steps. Although it takes some time to find a suitable solution, this reduces the computational workload and provides a filtering effect for measurement and numerical noise.

[0078] Alternatively, for example, a more powerful controller or general purpose processor may be used for monitoring, and / or other optimizers or optimization methods known to the skilled person may be employed. Such optimization methods may include simulated annealing, particle swarm optimization, or the use of general algorithms, etc. Although the computational workload of such optimization methods is much higher than that in the case of gradient optimizers, they may be useful, for example, to avoid local optima. Such optimization methods may also be used to optimize the parameters of more complex ECMs such as potential higher order models of battery-based pitch storage units.

[0079] In method step 166, the health state of the pitch storage unit 128 is calculated and optionally output. This is based on a comparison of the model parameters calculated in method step 164 with known reference values ​​at the end of the life of a given pitch storage unit 128. Such a health state value may represent the remaining life as a percentage value and may be used to plan the maintenance or replacement of the pitch storage unit 128. As described in further detail below, it may also be used for the operation of the pitch control system, for example to enable adaptive charging of the pitch storage unit 128.

[0080] Attention is paid to the fact that the described method 150 may be performed in a continuous manner throughout the operation of the wind turbine 100. In this case, the method steps 154 to 166 may be repeated in a loop structure. Note that in this case, the output model parameters calculated in the method step 164 may be used as the initial ECM parameter values ​​for the method step 154 ​​in the next iteration.

[0081] Note the fact that the physical parameters of the pitch storage unit 128 corresponding to the model parameters of the ECM usually change much slower than the time frame of the optimizer convergence. Therefore, after the optimizer reaches a minimum in one cycle or iteration of the optimization process, it can easily follow the physical parameter changes.

[0082] Figure 5 Shown is a Figure 3A The ECM 140 is used to estimate the health status of the pitch energy storage unit. As before, the method 170 may be performed during normal operation of the wind turbine 100.

[0083] The estimation loop begins at step 172. For example, the update of the health status may be triggered at regular intervals or when a specific event occurs. If the method is triggered for the first time, C, R i , R p The preconfigured values ​​are loaded into the estimator. The preconfigured values ​​can be taken from the component specifications as an initial guess. Otherwise, the estimator loads or retains the model parameters C, R from the previous estimation cycle. i , R p The value of .

[0084] In step 174 , the voltage u and the current i at the terminals 132 and 134 of the pitch energy storage unit 128 are measured. m Using the ECM 140 definitions and equations from above, the measured voltage can be used directly as the third sample value x3=u. Similarly, by calculating the voltage change x1=du / dt and the current change x2=di respectively m / dt to determine the first sample value and the second sample value.

[0085] In the case where the estimation cycle is performed at regular, relatively short intervals (e.g., every second), the time derivatives du / dt and di m / dt can be calculated by simply computing u from the last estimation cycle t and i m，t The current measurements and their respective predecessors u t-1 and i m，t-1 The difference between them is approximated, that is, x1 = du / dt = (u t -u t-1 ) / ΔT and x2=di m / dt=(i m，t -i m，t-1) / ΔT, where ΔT is the sampling interval between samples taken at time t-1 and t. In the case where the loop is performed at irregular and / or longer intervals, multiple measurements should be taken during step 174 and used to determine the current rate of change of the voltage and current. In other embodiments, numerical schemes for equal and unequal time intervals (e.g., time steps) can be applied to determine the rate of change of the voltage and current corresponding to different moments.

[0086] In step 176, the newly acquired sample is conditioned. This may include one or more of the following options.

[0087] As a first option, depending on the sampling frequency, filtering can be applied to smooth the sampling errors.

[0088] As a second option, at least in part by performing a quadruple analysis on each sample value (x1, x2, x3, i m ) is weighted to achieve regulation. For example, as mentioned above, the equivalent parallel resistance R p The effect on the optimization result may usually be small. To make it relevant for the optimization, possible errors are increased by high weighting factors. In addition, low weighting factors can be used to reduce the influence of samples with poor measurement quality. In the described embodiment, samples with large du / dt or di m Samples with / dt get a lower weighting factor. This is partly to reduce the effects of noise and partly because the capacitance of a capacitor is strongly frequency dependent.

[0089] As a third option, sample tuples (x1, x2, x3, i3) that are already contained in the same form or within a predefined tolerance interval of existing samples in the ring buffer may be rejected. m ), that is, the ring buffer is not entered for the second time.

[0090] In step 178, the method checks whether the sample list or sample set contains enough sample tuples to perform the optimization process. In the described embodiment, the optimization process uses a fixed number of samples, which are stored in a circular buffer of corresponding size. In this case, in step 178, it is verified whether all storage locations of the circular buffer are filled with valid samples.

[0091] If the sample list is still incomplete, ie if there is still unused space in the ring buffer, the newly acquired samples are added to the stored sample set in step 180. Thereafter, the current estimation cycle ends immediately, since there is not enough data available for optimization yet.

[0092] Otherwise, i.e., if a sufficient number of samples have been stored, the method proceeds in step 182 by removing the oldest previously stored sample from the sample list. The current sample is then stored at the end of the list. In the case of a circular buffer, this can be achieved by simply overwriting the corresponding storage location based on a circular indexing scheme.

[0093] In step 184, a starting point is selected for the optimizer. In a specific implementation, in order to combine computational efficiency and a stable output of the optimizer, this step can be performed in one of two possible ways. In particular, at regular intervals, for example, each x-th cycle starting from and including the first start-up of the optimizer, an initial parameter set can be used as a starting point for the optimization. As described above, the initial parameter set can be derived from the knowledge of the actual structure of the pitch energy storage unit 128. In addition to the characteristic values ​​contained in or derived from the component data table, these values ​​can also be updated based on, for example, the predicted aging of the energy storage device 130.

[0094] Alternatively, for example, at all other loops, the parameters obtained from the last loop of the estimation method 170 are used as the starting point for the optimizer run.

[0095] In step 186, the actual optimization is performed.

[0096] Note that a progressive optimizer is used, which performs the optimization using a discrete number of optimization steps, up to a predefined maximum number of steps, k. max .

[0097] In mathematical terms, the optimization process can be expressed as follows:

[0098] At step number k,

[0099] Optimization parameters at step k: a k

[0100] Note that the set of optimization parameters forms a vector a, and a k It refers to the vector with index k, starting from k=1.

[0101] Then, based on the optimizer "gradient" d k Calculate the RSS and RSS(a) of step k k ), as follows:

[0102]

[0103]

[0104] The optimizer uses a defined step size ρ to perform the next optimizer step, where a k+1 =a k+ρd k .

[0105] The step size p can be fixed, or optimized itself using a backtracking method. In the described implementation, a fixed step size p is used.

[0106] Note that step 186 may be performed in a repetitive manner, such as forming an inner loop, with the outer loop corresponding to Figure 5 As long as the current number of steps is less than the maximum number of steps, that is, k≤k max , the optimizer proceeds to the next optimization step in subprocess 186. Otherwise, subprocess 186 terminates and the current parameter value is used as the intermediate output of the current cycle of estimation method 170.

[0107] Note the fact that only a few optimization steps or even a single optimization step may be performed in each estimation cycle of the disclosed method 170. For example, in the described implementation, k max =1, meaning that only a single optimization step is performed during each execution of method step 186. When there is only one step, the optimizer effectively runs several cycles of the estimation method 170.

[0108] In step 188, a quality parameter of the new parameter estimate is determined. In the described embodiment, the RSS of the last optimization step is used as a quality parameter, such as a quality factor, and is stored in a separate variable, namely RSS_new = RSS(a k ).

[0109] In step 190 , the quality parameter RSS_new determined in step 188 of the current cycle is compared with the quality parameter RSS_last determined in step 188 of the previous estimation cycle of method 170 .

[0110] If it is determined that the newly calculated optimization parameter set a1, a2, and a3 from the optimizer is better than the previously used optimization parameter set, that is, if RSS_new<RSS_last, then the model parameters C, R of the ECM 140 are newly calculated based on the above equations. i and R p .

[0111] In the described implementation, C, R i and R p In particular, it is possible to verify that C, R i and R p Whether the newly calculated value of falls within the range of corresponding, for example, preconfigured reasonable parameter values.

[0112] If it is determined in step 190 that the new parameter values ​​are better and reasonable, then in step 192, the current optimization parameters a (e.g., vector (a1, a2, a3)) and model parameters (e.g., C, R) are rewritten with the last corresponding parameter sets obtained in steps 186 and 190, respectively. i and R p ).

[0113] Optionally, at this stage, appropriate filters may be applied before updating the stored parameter values, for example to prevent sudden changes in the corresponding parameter values.

[0114] Otherwise, if it is determined that the final parameter set is not better than the previously stored parameter set, then the newly calculated parameters are rejected in step 194 .

[0115] In either case, the cycle of the estimation method ends in step 196. If necessary, the current state of the estimator and / or optimizer is stored at this stage and used as initial value in the next estimation cycle.

[0116] At this stage, C and R can be output or recorded. i and R p The current model parameters of the estimator are used by other components, such as the adaptive charging method described later. Alternatively or additionally, an aggregate health state can be calculated based on one or more thresholds. Such an aggregate health state can be used to schedule and implement predictive maintenance. Note that, in general, the capacitance of a capacitor decreases over its lifetime, while its series resistance increases. Maintenance is only required when the corresponding model parameters output by the estimator are outside the allowed range for safe operation of the wind turbine 100.

[0117] For example, the start of life (BoL) threshold and the end of life (EoL) threshold may be provided based on the nominal values ​​provided in the data sheet of the component. In particular, the BoL capacitance C BoL It can be provided by the manufacturer of the capacitor used as the energy storage device 130. Then, the corresponding EoL capacitance C BoL can be calculated as, for example, C BoL 80% of the value, i.e. C EoL =0.8·C BoL The current state of health of the energy storage device 130 can be expressed as a percentage value relative to these values. Note that in practice, a capacitor may initially have a capacitance even higher than the nominal capacitance indicated in its data sheet. In this case, the capacitor's state of health will be greater than 100%. Conversely, if the capacitor is not replaced in time, its actual capacitance may drop to below C BoL , which will result in a negative health status value. Similar definitions and observations apply to the series resistor R i Or parallel resistance R pOne or more internal resistance values ​​to be compared. For example, the initial series resistance R of a capacitor BoL 200% of the series resistance R i The end-of-life value R EoL , that is, R EoL =2·R BoL .

[0118] In the described embodiment, the lower of the two percentage values ​​is considered as the overall health state. As soon as one of the two values ​​approaches, reaches or even falls below the corresponding EoL value, a predictive maintenance is scheduled, during which the entire pitch energy storage unit 128 or its internal energy storage device 130 is replaced. Note that a sudden drop below or above the corresponding threshold value may also allow the identification of a defective energy storage device 130.

[0119] To ensure that new relevant samples are regularly provided to the estimator, a controller (eg, pitch controller 124) executing method 170 may request a small charge or discharge of pitch energy storage unit 128. The frequency of these tests may depend on the quality of the last estimate measured by RSS as described above.

[0120] Figure 6 shows that the estimator is run continuously based on Figure 3A The ECM 140 shown in FIG. Figure 5 The method 170 is described to determine the relevant parameter values.

[0121] In particular, Figure 6 The upper portion of FIG. 1 shows the current i measured at terminals 132 and 134 of pitch energy storage unit 128 as a function of time. m A first graph 202 of voltage u and a second graph 204 of voltage u.

[0122] In the present example, pitch energy storage unit 128 comprises one or several capacitors which are initially fully discharged, for example when they are first connected to pitch converter 126. Thus, the voltage initially increases from zero to a predetermined first target voltage. During this first phase 206, the charging current is more or less constant.

[0123] In the second phase 208, the charging current drops to zero, for example due to a deliberate interruption of the charging cycle or due to an unexpected grid failure. Note that the pitch drive 122 is not activated in this phase. Therefore, the voltage u may only drop slowly and insignificantly in this phase, for example due to self-discharge of the capacitors or due to losses caused by the balancing network.

[0124] In a third phase 210 , the charging process continues with the same, more or less constant charging current until pitch energy storage unit 128 has reached a second target voltage at which the capacitor is substantially fully charged.

[0125] Therefore, the charging current i drops back to zero in the subsequent fourth phase 212 and remains substantially at zero.

[0126] Note that at this stage, the health state of the energy storage unit 128 may not yet be known because the estimator may not yet have sufficient data for optimizing the ECM 140. Therefore, the second target voltage may represent a default value for charging the energy storage unit 128.

[0127] In the fifth phase 214, the current i becomes negative, indicating a discharge operation. This may be caused by the operation of the pitch drive 122 when no or only an insufficient amount of electrical energy is available from the generator or the power supply grid. It can also be used to improve the results provided by the estimation method 170, for example by intentionally discharging the capacitor in a controlled manner. Therefore, the voltage u decreases during the fifth phase 214.

[0128] In a sixth phase 216, pitch drive 122 is deactivated and / or the controlled discharge is stopped, and pitch energy storage unit 128 is charged again. As a result, charging current i becomes positive and voltage u increases again, this time to a third target voltage.

[0129] Note that at this stage, the state of health of the energy storage unit 128 is already known because the estimator has now obtained enough data for optimizing the ECM 140. Therefore, the third target voltage may represent an optimized target voltage for charging the energy storage unit 128 based on the current state of health of the energy storage unit 128.

[0130] Figure 6 The middle portion of FIG. 2 shows a third graph 222 of the estimated capacitance C, the equivalent series resistance R, and the like as a function of time. i A fourth graph 224 of the error current and a fifth graph 226 of a root mean square (RMS) value (eg, the square root of the RSS value) of the quality parameter of the ECM 140. Note that the RMS value represents an estimated error based on the error current.

[0131] It can be seen that the estimator initially uses a first capacitance estimate that can be taken directly from a data table of capacitors included in the pitch energy storage unit 128. However, during optimization, this value increases to a second capacitance value during the second stage 208. At a later stage, the capacitance is further approximated and eventually sinks to a third capacitance value. Similar changes can be observed for the fourth graph 224 and the fifth graph 226, which show the gradual approximation of the corresponding model parameters as the estimator processes other samples.

[0132] Figure 6 The lower portion of 230 shows a sixth graph 232 of the estimated state of charge (SoC) of the pitch energy storage unit 128 indicated as a percentage value, a seventh graph 234 of the state of health (SoH) of the pitch energy storage unit 128 also indicated as a percentage value, and an eighth graph 236 of the internal temperature of the capacitor over time. Note that the SoC corresponds to the ratio of the current voltage to the target voltage, i.e., SoC=current voltage / target voltage.

[0133] Manual comparison with corresponding parameters determined by direct measurement or retrieved on the corresponding fieldbus of internal components of pitch energy storage unit 128 shows a good match of the estimated model parameter values ​​at least starting from fourth stage 212, e.g., after a complete charging operation of pitch energy storage unit 128.

[0134] As described above, the SoH that is aware of the pitch energy storage unit 128 is particularly able to perform system maintenance, including replacement of the pitch energy storage unit 128 or the energy storage device 130 contained therein, according to its specific requirements (e.g., just in time). Thus, an early replacement of an energy storage device that, for example, operates under less extreme conditions, is used less than expected, or has only a better quality than indicated in its data sheet, can be retired later in its life. Conversely, a storage device that, for example, operates under very harsh conditions, is used more than expected, or has only a lower quality than indicated in its data sheet, can be replaced earlier to avoid equipment failure.

[0135] Furthermore, according to another aspect of the present disclosure, a good understanding of the actual SoH of the pitch energy storage unit 128 or its internal components may also be used to actually extend its useful life by implementing an adaptive charging scheme as described in further detail below.

[0136] Depending on the type of energy storage device 130 used, adjusting the charging process and / or parameters can extend its life. In the following, an adaptive charging method for a capacitor-based pitch energy storage unit 128 is described as an example. However, similar methods can also be applied to other types of energy storage devices 130 such as rechargeable batteries.

[0137] Figure 7 1 shows a flow chart of an adaptive charging method 300. The method 300 is applicable to the above-mentioned Figure 1 The wind turbine 100 described above is similar to the wind turbine 100 described above. Figure 2 A pitch control system 120 is described.

[0138] In step 302, the current SoH of the pitch energy storage unit 128 or the energy storage device 130 contained therein is obtained. Note that the SoH may be obtained by the above method or any other suitable means that provides a good estimate of the SoH, including modeling the physical characteristics of its internal components based on other data including monitored environmental conditions and usage cycles.

[0139] In the described embodiment, the health status of the capacitor-based pitch energy storage unit 128 may be determined by Figure 3A The equivalent capacitance C and the equivalent series resistance R of the equivalent circuit 140 shown in FIG. i In this case, for example, if the capacitance C and / or the internal resistance R i If known during operation, the charging voltage may be varied during lifetime so as to always select the lowest possible charging voltage that still satisfies the desired load profile. The load profile may indicate a predetermined amount of electrical power and / or energy required to control the wind turbine 100 in an emergency situation. For example, the load profile may indicate the amount of electrical power required to brake the rotor 108 to a standstill.

[0140] Thus, in step 304, a determination is performed to verify whether the SoH of the pitch energy storage unit 128 satisfies at least one health criterion. Note that the health criterion may take the form of a single numerical threshold value such as an estimated SoC value indicated as a percentage. Alternatively, step 304 may include multiple individual determinations, such as verifying a combination of individual parameters obtained, for example, during the estimation.

[0141] In a specific example, the equivalent capacitance C and the equivalent series resistance R taken from the ECM 140 are i With the indicated equivalent capacitance C and equivalent series resistance R i The values ​​of the corresponding parameters at the end of their service life are compared.

[0142] In step 306, if the pitch energy storage unit 128 satisfies at least one health criterion, the pitch energy storage unit 128 is charged using a first charging method based on first charging parameters. The at least one health criterion may indicate that the pitch energy storage unit 128 is approaching its beginning of life (BoL), or at least closer than approaching its end of life (EoL).

[0143] In the described implementation, a first charging voltage (eg, 430 V) is used to charge the pitch energy storage unit 128 during the usage period toward the BoL.

[0144] Note that in the case of a capacitor-based pitch energy storage unit 128, pitch energy storage unit 128 is typically charged using a constant current until a desired target voltage is measured at both terminals 132 and 134. Thereafter, the desired target voltage is maintained, but the charging voltage drops to substantially zero.

[0145] In step 308, if the pitch energy storage unit 128 does not meet at least one of the health criteria, the pitch energy storage unit 128 is charged using a second charging method based on second charging parameters. Failure to meet at least one health criterion may indicate that the pitch energy storage unit 128 is nearing its end of life (EoL), or at least closer than near its beginning of life (BoL).

[0146] In the described implementation, when the equivalent capacitance C decreases and / or the series resistance R i When the voltage rises above the corresponding threshold, the charging voltage is increased. For example, at or near EoL, a second charging voltage such as 460V is used.

[0147] Note that in the disclosed implementation, the charging voltage increases linearly from the BoL value to the EoL value. Specifically, since the energy stored in a capacitor is proportional to both its voltage and capacity, the charging voltage increases in an inversely proportional manner with respect to the decrease in equivalent capacitance C, such that the amount of energy stored in a fully charged pitch energy storage unit 128 remains substantially constant during its lifetime.

[0148] Alternatively, in two corresponding parts of the entire life cycle, only two different charging parameter values ​​may be used, such as a charging voltage of 430 V or 460 V. In general, any number of charging parameter values, such as a charging voltage of 430 V, 440 V, 450 V or 460 V, may be used for corresponding numbers of the entire life cycle.

[0149] Note the fact that, due to the higher capacity near the BoL, the amount of energy stored in the pitch energy storage unit 128 during the first part of its service life is still sufficient for emergency operation at a lower charging voltage. At the same time, using a lower charging voltage reduces the stress on the capacitors contained therein, thus extending the service life of the pitch energy storage unit 128.

[0150] At least in the case where a capacitor is used as a storage element, the capacitance C and the resistance R i Typically depends on the temperature of the pitch energy storage unit 128. Typically, the capacitance 312 and resistance 314 of the capacitor are slightly better at higher temperatures, such as Figure 8 In addition, at higher temperatures, the internal storage devices 130 of the individual storage cells forming the pitch energy storage unit 128 age faster.

[0151] Note that the above methods 150 and 170 disclosed above for estimating the health state of the pitch energy storage unit 128 determine the equivalent capacitance C and the series resistance R i Thus, the adaptive charging method 300 will automatically select a lower charging voltage at higher temperatures (due to the higher capacitance and lower resistance obtained from the estimator), thereby at least partially compensating for the faster aging due to the higher temperature. Note that at least when the capacitance C and the resistance R are obtained from the estimator as described above, i In this case, no knowledge of actual age, charging and operating history or temperature is required to select the appropriate charging voltage.

[0152] In the case where the pitch energy storage unit 128 includes at least one rechargeable battery cell for pitch energy storage, charging the pitch energy storage unit 128 typically includes charging the rechargeable battery cell using a battery charging circuit or management system, which may be suitable for the type of battery used, such as a lithium battery. The battery charging circuit typically cuts off the charging voltage when the target voltage is reached, and short duty cycles may be repeatedly performed to maintain the desired charge level requested by the battery charging circuit or management system. In this case, the charging current, duration, or frequency of the battery charging circuit or management system may be updated based on the determined state of health.

[0153] Reference numerals

[0154] 100 wind turbines

[0155] 102 Tower

[0156] 104 Foundation

[0157] 106 Cabin

[0158] 108 Rotor

[0159] 110 Rotor Blades

[0160] 112 Rotor Hub

[0161] 120 Pitch Control System

[0162] 122 Pitch drive

[0163] 124 Pitch Controller

[0164] 126 Pitch converter

[0165] 128 Pitch Energy Storage Unit

[0166] 130 Energy storage device

[0167] 132 (first) terminal

[0168] 134 (Second) Terminal

[0169] 140 Equivalent Circuit Model (ECM)

[0170] 142 (measurement) nodes

[0171] 144 (reference) nodes

[0172] 146 (Equivalent) Capacitor

[0173] 148 (Equivalent) Series Resistor

[0174] 149 (Equivalent) Parallel Resistor

[0175] 150 Methods

[0176] 152-166 Methods and Steps

[0177] 170 Methods

[0178] 172-196 Methods and Steps

[0179] 202 First curve graph

[0180] 204 Second curve graph

[0181] 206 Phase 1

[0182] 208 Second Stage

[0183] 210 Phase 3

[0184] 212 Stage 4

[0185] 214 Stage 5

[0186] 216 Stage 6

[0187] 222 The third curve

[0188] 224 Fourth Curve

[0189] 226 Fifth Curve

[0190] 232 Sixth Curve

[0191] 234 Seventh Curve

[0192] 236 Eighth Curve

[0193] 240 First-order ECM

[0194] 250 n-order ECM

[0195] 300 Methods

[0196] 302-308 Methods and Steps

[0197] Voltage

[0198] i m Measuring current

[0199] i s Calculate current

[0200] C (equivalent) capacitance

[0201] R i (Equivalent) Series Resistance

[0202] R p (Equivalent) Parallel Resistance

Claims

1. A method (150) for estimating a health state of a pitch energy storage unit (128) of a wind turbine (100), the method (150) comprising: - providing (152) an equivalent circuit model (140) ECM of the pitch energy storage unit (128), the ECM (140) comprising at least at least one electrical energy storage element connected between two power supply terminals (132, 134) and an equivalent series resistor (148); - repeatedly sampling (156, 158) the voltage u and the corresponding current im at the two power supply terminals (132, 134); - determining (160, 162) at least one voltage change and at least one current change for a plurality of voltage samples and corresponding current samples; - performing (164) an optimization process based at least on the ECM (140), the plurality of voltage samples, the plurality of current samples, the determined voltage variation and the determined current variation to obtain an updated resistance Ri of the equivalent series resistor (148) and an updated at least one model parameter of the at least one electrical energy storage element; as well as - estimating (166) at least one health status parameter of the pitch energy storage unit (128) by comparing at least one of the updated resistance Ri and the updated at least one model parameter with at least one threshold value.

2. The method (150) of claim 1, wherein: - The optimization process is based on a predetermined number of sample tuples (x1, x2, x3, i m ), each sample tuple (x1, x2, x3, i m ) includes the current voltage sample (u=x3), the corresponding time derivative of the voltage u (x1=du / dt), the current current sample i m and current i m The corresponding time derivative of (x2 = dim / dt); and -When a predetermined number of sample tuples (x1, x2, x3, i m ) is already stored in the buffer storage device, the optimization process is performed.

3. The method (150) of claim 2, further comprising: - Determine whether the current sample tuple satisfies at least one predetermined filtering criterion, in particular, determine whether the current sample tuple (x1, x2, x3, i m ) are different from all sample tuples contained in the buffer storage device; as well as - If the at least one predetermined filtering criterion is met, the current sample tuple (x1, x2, x3, i m ) is added to the buffer storage device, otherwise, the current sample tuple (x1, x2, x3, i m ).

4. The method (150) of claim 1, wherein: The optimization process is performed multiple times, and the method (150) further includes: - selecting (154, 184) starting values ​​for a set of optimization parameters optimized by the optimization process; - determining (188) at least one quality parameter RSS associated with an updated value of said set of optimization parameters obtained after executing said optimization process starting from said starting values nev ;as well as - If at least one quality parameter RSS associated with the set of optimization parameters nev If at least one quality condition is met, an updated resistance of the equivalent series resistor (148) and an updated at least one model parameter of the at least one energy storage element are calculated (192), otherwise the previously calculated resistance of the equivalent series resistor (148) and the at least one model parameter of the at least one energy storage element are maintained.

5. The method (150) of claim 4, wherein: Selecting the starting value for the set of optimization parameters includes at least one of: - selecting a predefined set of initial starting values, in particular when performing said optimization procedure for the first time or after performing said optimization procedure a predetermined number of times; or - When executing the optimization process, the update value obtained at a previous time is selected.

6. The method (150) of claim 4, wherein: - Each time the optimization process is performed, the residual sum of squares RSS is calculated as RSS = || Aa-I m || 2 , wherein A corresponds to a matrix including sample values ​​of the plurality of voltage samples (x3=u) and the corresponding time derivative of the voltage (x1=du / dt) and the corresponding derivative of the current (x2=di / dt), a corresponds to a vector of the optimization parameters, and I m The vector corresponding to the sampled current; - the at least one quality parameter RSS nev corresponds to the RSS; and - said at least one quality condition comprises determining whether the calculated RSS is less than an RSS calculated in a previous iteration of said optimization process.

7. The method (150) of claim 6, wherein: - performing said optimization process using a gradient optimizer, - The gradient optimizer performs up to k max There are k optimization steps, where max ≥1; -The gradient optimizer minimizes the RSS.

8. The method (150) of claim 1, wherein: The step of estimating (166) the health status of the pitch energy storage unit (128) comprises at least one of: - comparing the updated at least one model parameter of the at least one electrical energy storage element with a nominal parameter value of the at least one electrical energy storage element, in particular with a predetermined multiple of the nominal parameter value; as well as - comparing the updated resistance Ri with a nominal resistance value of the equivalent series resistor (148), in particular with a predetermined multiple of the nominal resistance.

9. The method according to claim 1, further comprising: - requesting at least one of a controlled charging or discharging event of the pitch energy storage unit, in particular using a predetermined charging or discharging current; as well as - the voltage u and the corresponding current i at the two power supply terminals (132, 134) during the controlled charging or discharging event m At least one sampling is performed (156, 158).

10. The method (150) of claim 1, wherein: The pitch energy storage unit (128) comprises at least one capacitor for pitch energy storage, in particular an ultracapacitor, at least one energy storage element of the ECM (140) comprises an equivalent capacitor (146), and the updated parameter corresponds to an updated capacitance C of the equivalent capacitor (146).

11. The method (150) of claim 10, wherein: The ECM (140) further includes an equivalent parallel resistor (149) having a resistance Rp connected in parallel with the equivalent capacitor (146), wherein a total modeled current i in the ECM (140) s Defined by the following equation: i s :=C / (1+R i / R p )du / dt-CR i (1+R i / R p )di m / dt+1 / (R p +R i )u。 12. The method (150) of claim 10, further comprising: - if the health state indicates that the pitch energy storage unit is at or near its beginning of life BoL, charging the capacitor to a first charging voltage sufficient to provide a predetermined amount of electrical power and / or energy; as well as - If the health state indicates that the pitch energy storage unit is at or near its end of life EoL, charging the capacitor to a second charging voltage sufficient to provide a predetermined amount of electrical power and / or energy, wherein the second charging voltage exceeds the first charging voltage.

13. The method (150) of claim 12, wherein: The health state indicates an estimated capacitance C of the capacitor, and a charging voltage of the capacitor increases from the first charging voltage to the second charging voltage based on the estimated capacitance C, specifically increases from the first charging voltage to the second charging voltage in an inversely proportional ratio.

14. The method (150) of claim 1, wherein: The pitch energy storage unit (128) includes at least one rechargeable battery unit for pitch energy storage, at least one electrical energy storage element of the ECM includes an equivalent voltage source, and the updated parameter corresponds to a voltage of the equivalent voltage source.

15. A pitch control system (120) for a wind turbine (100), the wind turbine (100) comprising an energy storage unit and a converter circuit, in particular a pitch energy storage unit (128) and a pitch converter (126), wherein: - the energy storage unit comprises at least one energy storage device (130) and has at least two power supply terminals (132, 134) for receiving or providing electrical energy; - the converter circuit is connected to the energy storage unit via the at least two power supply terminals (132, 134) to selectively charge or discharge at least one energy storage device (130) of the energy storage unit; and The pitch control system (120) further comprises at least one controller, in particular a controller (124) of the converter circuit, the at least one controller (124) being configured to implement the method according to any one of claims 1 to 14.

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