Improvements relating to wind turbine blade anti-icing systems

Abstract

A method of controlling a wind turbine blade anti-icing system, the system comprising a power supply and a plurality of electric blade heating devices. The method comprises: energizing a selected one of the blade heating devices; measuring one or more electrical parameters associated with the selected one of the blade heating devices; determining the power draw of the selected one of the blade heating devices based on the one or more measured electrical parameters; and controlling the selected one of the blade heating devices based on the determined power draw. Advantageously, the method of the present invention provides for in-situ calibration of the electric heating devices during operation of the anti-icing system. Thus, the performance of the heating devices can be evaluated under predetermined input power supply conditions, which allows the anti-icing system to be more effectively controlled.

Description

Technical Field

[0001] The present invention relates to an anti-icing system for a wind turbine blade and to a method for controlling such an anti-icing system. The present invention also relates to a wind turbine and indeed a wind turbine blade incorporating such an anti-icing system. Background Art

[0002] Wind turbines may need to operate in geographic areas that experience very cold climatic conditions during at least part of the year. Although the system components of wind turbines are designed to operate in a variety of adverse climatic conditions, it is a well-known problem that icing of wind turbine blades can have an adverse effect on the power generation efficiency of the wind turbine. Ice accumulation on wind turbine blades increases blade mass, but it also changes the aerodynamic profile of the blades, thus making them a less efficient airfoil. This results in the rotor producing less torque at a given wind speed, and therefore reduced power generation potential.

[0003] Various methods have been developed to remove ice from wind turbine blades. For example, shaking devices may be mounted on the blades in an effort to impart violent oscillations to the blade structure in order to physically shake the ice off the blades.

[0004] Another approach is to implement an electrical heating system in or within the blade. For example, it is known to blow heated air into the hollow interior of a blade in order to raise the temperature of the blade surface sufficiently to prevent or reduce ice accumulation. Another approach is to integrate electrical heating elements into the blade surface, and such systems are often successful in preventing ice accumulation. However, electrical heating elements tend to be very power hungry, which makes it a challenge to effectively control them to prevent ice buildup while keeping power flow within the limits determined by the electrical transmission system within the hub. In addition, typically a blade will be equipped with several different heating devices spaced around the blade surface to provide heating in selected areas on the blade. Due to manufacturing issues, the electrical and mechanical characteristics of the heating devices vary from device to device, which creates further challenges in how the anti-icing system is controlled.

[0005] It is to address some of these issues that embodiments of the present invention are designed. Summary of the invention

[0006] In this context, the present invention provides a method of controlling a wind turbine blade anti-icing system, the anti-icing system comprising a power supply and a plurality of electric blade heating devices. The method comprises: energizing a selected one of the blade heating devices; measuring one or more electrical parameters associated with the selected one of the blade heating devices; determining the power of the selected one of the blade heating devices based on the one or more measured electrical parameters; and controlling the selected one of the blade heating devices based on the determined power draw.

[0007] Advantageously, the method of the present invention provides for in-situ calibration of the electric heating device during operation of the anti-icing system. Thus, the performance of the heating device can be evaluated under predetermined input power supply conditions, which allows the anti-icing system to be more effectively controlled.

[0008] The steps of energizing, measuring and determining may be performed sequentially for each of the plurality of blade heating devices. In this manner, calibration may be performed individually for each of the heating devices using a smaller set of sensors. The calibration process may be run sequentially for each heating device and substantially immediately one after the other. Alternatively, the calibration process may be scheduled for each heating device at a predetermined time.

[0009] The step of energizing a selected one of the blade heating devices may include activating a switch to provide power to the blade heating device. Thus, the calibration process may focus on one heating device at a time.

[0010] The step of measuring electrical parameters associated with the selected blade heating device may include varying the energization of the blade heating device to cause a change in the one or more measured electrical parameters. For example, the applied voltage of the heating device may be varied to evaluate the performance of the heating device under a range of current loads.

[0011] The measured electrical parameters may include a voltage applied to a selected blade heating device and a current associated with the selected heating device. Likewise, measuring the current through a selected one of the blade heating devices may include making an input current measurement and an output current measurement with respect to the blade heating device.

[0012] The step of controlling the selected blade heating device may include determining a maximum on time of the selected blade heating device based at least in part on the determined power draw. Alternatively, or in addition, the step of controlling the selected blade heating device may include analyzing the determined electrical parameter and / or the determined power over an extended period of time to provide a diagnostic function.

[0013] The present invention also extends to a wind turbine comprising: a plurality of wind turbine blades; a blade anti-icing system comprising a plurality of blade heating devices; and a control system for controlling and providing power to the plurality of blade heating devices, the wind turbine further comprising a sensing device for sensing electrical parameters associated with the plurality of blade heating devices, and wherein the control system is operable to: energize a selected one of the blade heating devices; measure the electrical parameters of the selected one of the blade heating devices; determine the power of the heating device based on the measured electrical parameters; and control the heating device based on the determined power of the heating device. The control system comprises a switch module, the switch module comprising a plurality of switch devices, each switch device being associated with a respective blade heating device, wherein the control system is operable to selectively operate one of the switch devices to selectively energize the associated blade heating device.

[0014] The sensing means may comprise a voltage sensor for measuring an applied voltage between a current supply line associated with the blade heating device and a current return line from the blade heating device. The sensing means may also comprise a current sensor on the current supply line and / or a current sensor on the current return line.

[0015] It is expressly intended that within the scope of the present application, the various aspects, embodiments, examples and alternatives listed in the preceding paragraphs, claims and / or the following description and drawings, and in particular the individual features thereof, may operate independently or in any combination. That is, all embodiments and / or features of any embodiment may be combined in any manner and / or combination unless such features are incompatible. Applicants reserve the right to change any originally filed claims accordingly or to file any new claims, including the right to amend any originally filed claim to be subordinate to any other claim and / or to incorporate any features of any other claim, even though not originally claimed in this manner. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] One or more embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0017] Figure 1 is a perspective view of a wind turbine including a nacelle, a hub and a set of blades, in which embodiments of the present invention may be implemented;

[0018] Figure 2 is a schematic diagram of a blade anti-icing system according to an embodiment of the present invention;

[0019] Figure 3 is a flow chart depicting a method according to one embodiment of the present invention. DETAILED DESCRIPTION

[0020] Specific embodiments of the invention will now be described, wherein many features will be discussed in detail to provide a thorough understanding of the inventive concepts defined in the claims. However, it will be apparent to those skilled in the art that the invention may be practiced without this specific detail, and in some cases, well-known methods, techniques, and structures have not been described in detail to avoid unnecessarily obscuring the invention.

[0021] In order to place the embodiments of the present invention into proper context, reference is first made to Figure 1 , which shows a portion of a typical horizontal axis wind turbine 2 (HAWT), in which embodiments of the present invention may be implemented.

[0022] In general, the wind turbine 2 includes a nacelle 4 rotatably coupled to the top of a tower 6 so that the nacelle 4 can rotate left and right relative to the tower 6. Figure 1 Although not shown, the wind turbine 2 is mounted on a suitable base, which may be onshore or offshore, depending on the installation requirements. Both installation methods are familiar to the skilled person.

[0023] In the general case, the nacelle 4 supports a rotor hub 8 to which a set of wind turbine blades 10 are coupled. The wind turbine shown includes three blades, although it will be understood that this is only an example and that a different number of blades is acceptable. In the general case, the wind flow acts on the blades 10, generating a torque on the rotor hub 8, thereby rotating the rotor hub 8 and transmitting the rotational movement to the power generation equipment housed in the nacelle 4. The nacelle 4 houses many of the power generation components of the wind turbine 2, including a generator, a gearbox, a drive train and a brake assembly, as well as a converter and other electrical equipment for converting the mechanical energy of the wind into electrical energy to be provided to the grid. Such components are conventional, so further details are omitted so as not to obscure the reader of the present invention.

[0024] A wind turbine includes an electrical system, a portion of which is Figure 1 20 is shown as a blade anti-icing system. At this point, it should be understood that the electrical system of the wind turbine is shown in schematic form and is therefore simplified for the purposes of this description. In particular, the focus of this discussion is the anti-icing system (which is shown in FIG. Figure 1 ), rather than other electrical systems and components of the wind turbine, which are not shown or discussed here for clarity, but which are present in actual embodiments.

[0025] As mentioned above, cold weather conditions can cause ice to accumulate on the blades during operation, a phenomenon that can have an adverse effect on power generation. This is primarily because the accumulation of ice changes the airfoil profile of the blades, making them less efficient at generating torque at a given wind speed. As a result, as ice accumulates, the power generation of the wind turbine steadily decreases. The wind turbine's control system can detect this gradual loss of power generation and can be used as a trigger to activate the anti-icing system.

[0026] The anti-icing system 20 provides a method of combating ice accumulation on the surface of the blade. To this end, the anti-icing system 20 can use one or more heating devices to apply heat to the blade surface under various triggering conditions. For example, when a certain ice threshold is detected, activation of the anti-icing system can occur. The power supply to the heating device can be adjusted in various ways to achieve the desired reduction in ice. For example, the power supply can be gradually applied to the heating device based on the temperature of the outer surface of the blade detected or modeled. Alternatively, in order to achieve the purpose of reducing ice, power can be supplied to the heating device at a maximum level for a predetermined time period. This power strategy can be applied periodically to keep the blades free of ice.

[0027] In general, the anti-icing system 20 comprises a plurality of electric surface heating devices 22 which are electrically connected to a power and control system 24. The heating devices or "elements" 22 may be in the form of conductive mats, panels, networks or pads, all of which are well known in the art. Alternatively, the electric heating device 22 may be a length of resistive cable which is wound or laid over an appropriate area of ​​the blade surface in order to generate heat at a desired location. One type of suitable electric heating device is known from WO 2017 / 108064 which discloses an electric heating device in the form of a glass fiber mat coated with conductive carbon.

[0028] In the embodiment shown, three heating devices 22 are provided at spaced locations along the blade. Figure 1 As shown, the spacing of the heating devices 22 is for convenience only and does not indicate a specific spacing within the blade. Typically, more than three heating devices will be provided, although this is not necessary, and the heating devices may have an optimized spacing different from the spacing shown here. For example, 10 to 40 heating devices may be incorporated into the blade, distributed between the windward surface and the leeward surface. Certain arrangements of the heating devices may be designed in which less critical or vulnerable areas of the blade (such as areas near the root of the blade) are not provided with heating devices. However, it should be noted at this point that the spacing of the heating devices is not core to the present invention, and the aforementioned arrangements are provided only as examples.

[0029] Still Figure 1According to the system diagram, the power and control system 24 of the heating device 22 generally includes a blade power control module 26, a hub power control module 28, a power transmission device 30, a power source or power source 32 and a system controller 34. It should be understood at this time that the anti-icing system 20 is shown here for only one blade. In practice, each blade has suitable components to heat the blade. The various electrical and electronic components mentioned above are appropriately connected together through suitable power and control cables and / or busbars to transmit power and control signals between the corresponding components as needed.

[0030] The power transmission device 30 is a rotating interface between the rotating hub 8 and the fixed nacelle 4. Such components are conventional, so a full discussion is not required here. However, such components generally take the form of a slip ring device that is capable of transmitting power from a nacelle-based power input and providing a power output to the rotating structure of the hub to supply power to any power consumers located in the hub. One such power consumer is the hub-based component of the anti-icing system 20.

[0031] The power transmission device 30 can transmit direct current and / or alternating current. Usually, the alternating current will be transmitted in single-phase or three-phase form.

[0032] The power transfer device 30 is also capable of transmitting electronic signals across the rotating interface. Thus, the power transfer device 30 is shown here as receiving a first input from a power source 32 and a second input from a system controller 34.

[0033] Conversely, the power transmission device 30 provides an output 40 to the hub power control module 28. The output 40 provides power, but may also provide electronic signals. It should be noted that while the electronic control signals may be transmitted via a hardwired network, these electronic control signals may also be transmitted by way of a wireless network.

[0034] The system controller 34 controls the operation of the anti-icing system 20 and can be embodied in different ways. As shown, the system controller 34 is located in the nacelle 4. However, this is not required, and the system controller 34 can also be located in the rotor hub 8. In addition, the functions provided by the system controller 34 can be provided by the main wind turbine controller (not shown), or the system controller 34 can be a dedicated control unit used only for controlling the anti-icing system. Regardless of the physical location of the system controller 34, it is understood that it provides a suitable processing environment and associated computing, storage and input / output components to control and communicate with the various components of the anti-icing system.

[0035] System controller 34 receives input (not shown) regarding the operation of the wind turbine and its operating environment, and performs processing to determine a desired activation strategy for electrical heating devices 22. For example, based on measured or modeled outside air temperature and power generation values, system controller 34 may determine that at least one of electrical heating devices 22 should be activated.

[0036] The time at which the one or more heating devices 22 are activated may be further determined. For example, the system controller 34 may instruct the electric heating device to operate for a predetermined period of time to generate a predetermined thermal power output. In addition, the system controller 34 may instruct the activation duty cycle to be implemented to maintain a predetermined average power output. Such a strategy is described in WO2017 / 108064.

[0037] A hub power control module 28 is located in the hub 8 and provides power distribution functions for the anti-icing system components located in the blades. The hub power control module 28 receives input from the power transmission module 30 and distributes electrical energy to the heating devices 22. The precise configuration of the hub power control module 28 is not central to the present invention and is conventional in general form. However, it should be able to selectively distribute power to the heating devices within the blades.

[0038] The blade power control module 26 has the function of receiving power input from the hub power control module 28 and distributing the power among the electric heating devices 22 within the corresponding blade. Therefore, each blade power control module 26 incorporates the required switch units and sensors to selectively activate and monitor the electric heating devices 22.

[0039] Figure 2 Features of the blade power control module 26 and the electric heating devices 22 are shown in more detail. Here, the blade power control module 26 comprises a switch unit 50 which selectively supplies power to the three blade heating devices 22 .

[0040] One challenge associated with the goal of powering and controlling these electrical heating devices is that the electrical characteristics may vary from device to device. Typically, this is due to material differences that occur during the manufacturing process. For example, it has been observed that heating pads using carbon fiber based conductive materials exhibit approximately 5-10% variation in resistance from device to device. This variation can have a significant impact on the current drawn by each heating device at a predetermined applied voltage. When considered in the context that the entire anti-icing system may have a rated power draw potential of approximately 50kW or more, a 5-10% variation in the resistance of the heating pad is significant. This variation is typically accounted for when designing the system to ensure that the system does not exceed safety limits. However, this will result in a system that is not ideal in performance and is not uniform in application.

[0041] To guard against these problems, embodiments of the present invention provide a system and a control process that are configured to quantify and adapt to changes in electrical characteristics to ensure proper operation.

[0042] Reference Figure 2 , the switch unit 50 is shown as being under the control of the system controller 42 and therefore receiving control signal inputs therefrom. Based on these control inputs, the switch unit 50 is operable to control the current flowing to each heating device 22 connected thereto. In addition to communicating control signals to the switch unit 50, the system controller 34 also receives data signals from sensing devices associated with the anti-icing system 20. Here, the sensing devices sense electrical parameters associated with the input voltage and current of the electric heating devices 22.

[0043] from Figure 2 As can be seen in the figure, the blade power control module 26 includes an input current line 52, and an output current or "ground" line 54. The input current line 52 is connected to the power input terminal 56 of each of the electric heating devices 22 through the switch unit 50. For clarity, Figure 2 Only two power inputs 56 are marked. Electrical switches 57 are provided by the switch unit 50 to provide control of the activation of each of the electric heating devices 22. In the embodiment shown, each switch 57 is associated with a single electric heating device 22. However, it should be noted that the switch 57 can also be associated with a group of heating devices. It is envisioned that electronically controlled semiconductor switches are most suitable, although other switch configurations are also acceptable. It should be noted at this point that the system controller 34 can control the switch 57 through an appropriate communication link with the blade power control module 26.

[0044] The output current line 54 is connected to the power return connection 58 of each electric heating device 22 (only one of which is shown here for clarity), thus providing a neutral connection. It can therefore be understood that current can flow along the input current line 52, through the switch unit 50, and to the power input 56 of the heating device. From there, the current flows from the power return connection 58 to the output current line 54.

[0045] In order to monitor the power flowing to the electric heating device 22, the blade power control module 26 is provided with a first current sensor 60 and a second current sensor 62. It should be noted at this point that these two current sensors are not required to monitor the current flowing through the device, as a single current sensor on the input or output current line 52, 54 is sufficient. However, the provision of two current sensing devices provides redundancy and is also a means for the control system to verify the correct function of the two sensors.

[0046] The first current sensor 60 is configured and arranged to monitor the current flowing through the input current line 52. Similarly, the second current sensor 62 is associated with the output current line 54 for monitoring the current flowing through the output current line 54. Any suitable current sensor / transducer is acceptable (e.g., current sensors / transducers based on Hall effect, inductive or magnetoresistive sensing principles).

[0047] In addition to the two current sensors, a voltage sensor 70 is provided. The voltage sensor is arranged and configured to measure the applied voltage between the input current line 52 and the output current line 54. In a similar manner to the current sensors, any suitable voltage sensor (such as a resistive or capacitive voltage sensor) may be used.

[0048] Although not shown here, it should be understood that the first and second current sensors 60, 62 and the voltage sensor 70 are configured to communicate with the system controller 34 to provide it with measurements regarding the performance of the heating device 22. To this end, these sensors may be coupled to the system controller 34 via a wired or wireless connection.

[0049] By providing the current sensors 60, 62 and the voltage sensor 70, the system controller 34 is able to measure the actual current flowing through the heating device 22 and therefore also be able to calculate the actual electrical power being dissipated, which will be proportional to the heating power. Thus, beneficially, the system controller 34 is able to perform a calibration process to determine the actual power drawn by the electric heating device 22 compared to the expected power draw based on its theoretical electrical specifications.

[0050] The system controller 34 is configured to operate each switch 57 of the switch unit 50 so as to activate a selected one of the electric heating devices 22 for calibration. For example, to calibrate the first electric heating device 22 (specifically identified by label Pz), the system controller 34 will configure the uppermost switch 57 to a closed position and the middle switch 57 and the lowermost switch 57 to an open position. Since only one electric heating device 22 is activated, the voltage applied is only across that single switch, so current will flow from the input current line 52, through the single switch 57 and the electric heating device 22, and to the output current line 54. Therefore, the system controller 34 is able to monitor the voltage sensor 70 and any of the two current sensors 60, 62, and determine the electrical power consumed by the electric heating device (based on the relationship P=VI), and also determine the power dissipated by the electric heating device as heat energy (based on the relationship P=I 2 R).

[0051] The system controller 34 may perform the calibration process at repetitive time intervals. For example, the process may be performed when the wind turbine is started up after a maintenance event. Alternatively, the process may be performed based on a predetermined schedule, or in accordance with a manually triggered instruction (e.g., manually triggered via a SCADA interface with a wind turbine master control center). Thus, in accordance with the above discussion, the system controller 34 implements a dynamic calibration process for the electrical heating devices 22, wherein selected heating devices may be selected in turn to collect data on associated electrical characteristics, by which the devices may be more effectively controlled.

[0052] The calibration process may include calibrating all of the electric heating devices 22 during a single period of time. However, since this may take a considerable amount of time, one option is to implement a "rolling calibration process" in which the system controller 34 calibrates the electric heating devices 22 in a cyclic manner.

[0053] Using the calibrated electrical parameters of the electric heating devices 22, the system controller 34 is able to calculate an accurate measurement of the electrical power drawn by each electric heating device 22 when activated with a given supply voltage. Thus, the system controller 34 can store the calibrated electrical parameters in appropriate processor memory for use in subsequent calculations related to the safe operation of the electric heating devices 22.

[0054] The above procedure can be represented as a process flow chart. Figure 3 It can be considered that the system controller 34 implements the functions expressed by the control process 100, through which the system controller can more accurately determine the electrical characteristics of the anti-icing system and thus can more effectively control the anti-icing system.

[0055] The control process 100 begins at step 102, in which the system controller 34 energizes the selected heating device 22. As described above, it is contemplated that one of the electric heating devices 22 is activated at a time so that the voltage and current are measured with respect to that heating device. However, it should be noted that a more complex, and therefore more expensive, and potentially less reliable sensing mechanism can be contemplated that enables multiple electrical devices to be analyzed simultaneously. For example, current and voltage sensors can be installed on the respective power return connection 58 associated with each heating device, or on the respective connection lines 58a extending to the main power return line 64.

[0056] Once the selected heating device 22 is activated, the system controller 34 can determine the voltage applied to the selected electric heating device 22 and the current it draws at step 104. Appropriately, these parameters can be stored in memory for later use. In addition, these determined parameters can be stored in an appropriate log, as this may be useful for long-term diagnosis of the health of the heating device.

[0057] Once the voltage and current associated with the selected electric heating device 22 are determined, the system controller 34 can calculate the necessary electrical characteristics of the heating device 22 at step 106. For example, this may be the power draw for a predetermined voltage. Thus, during a calibration process, the system controller 34 may activate the heating device with a series of discrete applied voltages and determine the power draw at each voltage level.

[0058] Finally, the system controller 34 may be operable to control the anti-icing system based on the determined characteristics of the selected electric heating device at step 108. It should be noted that the process 100 may be repeated for different electric heating devices.

[0059] In controlling the electrical heating device, the system controller 34 may use the determined electrical characteristics in the following non-limiting use cases:

[0060] - The system controller 34 can calculate the maximum "on time" that the electric heating device 22 can be activated without negatively affecting the power supply equipment or causing an over-temperature condition in the blade. Therefore, the calculated maximum on time can be implemented as an automatic reset threshold time period, which, if exceeded, will trigger the deactivation of the electric heating device 22.

[0061] The system controller 34 can also implement a more reliable maximum power threshold. Since the system controller 34 can calculate the actual power draw of each electrical device, it can accurately track the total power draw of the electrical devices, for example to ensure that the total power draw does not exceed the power limit of the power transfer device 30.

[0062] - Using the calibrated electrical parameters, the system controller 34 is able to calculate a more accurate "on time" for the electrical device based on a predetermined applied voltage to achieve the desired heat output of the device. Therefore, if the electrical heating device is configured such that it draws less power than its "rated" specification, the system controller 34 is able to extend the on time to provide the desired heating effect to the device, thereby improving the operation and uniformity of the anti-icing system.

[0063] - The system controller 34 can perform trend calculations on multiple calibration processes to monitor the performance of the electric heating equipment. Abnormal readings can be reported to the operator through the error log or SCADA interface.

[0064] The present invention has been described above by way of example by discussing the illustrated embodiments. Some variations of the specific embodiments have been mentioned above, but the skilled person will appreciate that other variations and modifications not mentioned may be made to the specific embodiments without departing from the scope of the invention as defined in the claims.

Claims

1. A method of controlling a wind turbine blade anti-icing system, the system comprising a power source and a plurality of electric blade heating devices, wherein the method comprises: energizing a selected one of the blade heating devices; measuring one or more electrical parameters associated with the selected one of the blade heating devices; determining a power draw of the selected one blade heating device based on one or more measured electrical parameters; as well as controlling the selected one blade heating device based on the determined power draw, wherein controlling the selected blade heating device includes determining a maximum on time of the selected blade heating device based at least in part on the determined power draw, and Wherein, the method further comprises: determining whether the determined power draw is less than a rated power draw of a selected blade heating device; and In response to the determined power draw being less than a rated power draw of the selected blade heating device, the maximum on time of the selected blade heating device is extended.

2. The method according to claim 1, wherein: The steps of energizing, measuring, and determining are performed sequentially for each of the plurality of blade heating devices.

3. The method according to claim 1 or 2, wherein: The step of energizing a selected one of the blade heating devices includes activating a switch to provide power to the blade heating device.

4. The method according to claim 1 or 2, wherein: The step of measuring electrical parameters associated with the selected blade heating device includes varying energization of the blade heating device to cause a change in one or more measured electrical parameters.

5. The method according to claim 1 or 2, wherein: The electrical parameters measured include the voltage applied to the selected blade heating device and the current associated with the selected blade heating device.

6. The method according to claim 5, wherein: Measuring the current through the selected one of the blade heating devices includes making an input current measurement and an output current measurement with respect to the blade heating device.

7. The method according to claim 1 or 2, wherein: Controlling the selected blade heating device includes analyzing the determined electrical parameter and / or the determined power over an extended period of time to provide a diagnostic function.

8. A wind turbine comprising: a plurality of wind turbine blades; a blade anti-icing system including multiple blade heating devices; a control system for controlling and providing power to the plurality of blade heating devices, and sensing means for sensing electrical parameters associated with the plurality of blade heating devices, wherein the control system is operable to: energize a selected one of the blade heating devices; measure electrical parameters of the selected one of the blade heating devices; determine a power draw of the selected blade heating device based on the measured electrical parameters; and control the selected blade heating device based on the determined power draw, wherein when controlling the selected blade heating device, the control system is further operable to determine a maximum on time of the selected blade heating device based at least in part on the determined power draw, and The control system may also be operable to: determine whether the determined power draw is less than the rated power draw of the selected blade heating device; and in response to the determined power draw being less than the rated power draw of the selected blade heating device, extend the maximum on time of the selected blade heating device.

9. The wind turbine according to claim 8, wherein: The control system includes a switch module including a plurality of switch devices, each switch device being associated with a respective blade heating device, wherein the control system is operable to selectively operate one of the switch devices to selectively energize the associated blade heating device.

10. A wind turbine according to claim 8 or 9, wherein: The sensing means comprises a voltage sensor for measuring an applied voltage between a current supply line associated with a blade heating device and a current return line from the blade heating device.

11. The wind turbine according to claim 10, wherein: The sensing device further comprises a current sensor on the current supply line and / or a current sensor on the current return line.

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