Safety device and method for a wind turbine

Field of Invention

The present invention relates to the field of wind turbines, in particular to a safety device for switching a wind turbine between a safe mode of operation and a normal mode of opera tion. The present invention further relates to a wind turbine comprising a safety device, a wind farm comprising a plurali ty of wind turbines, a method of switching a wind turbine be tween a safe mode of operation and a normal mode of opera tion, and a computer program.

Art Background

When a technician enters a wind turbine, care must be taken that the wind turbine does not operate in a way that exposes the technician to danger. A dangerous situation could for ex ample occur if a wind farm controller erroneously sets the wind turbine to operate at full (rated) power while the tech nician is working on the turbine.

Accordingly, there may be a need for a 100% reliable way of setting a wind turbine to operate in a safe mode while the technician is working.

Summary of the Invention

This need may be met by the subject matter according to the independent claims. Advantageous embodiments of the present invention are described by the dependent claims.

According to a first aspect of the invention, there is pro vided a safety device for switching a wind turbine between a safe mode of operation and a normal mode of operation. The safety device comprises (a) a controller comprising a first pair of terminals, a second pair of terminals, and control logic, the control logic being adapted to generate an output signal indicative of either the safe mode of operation or the normal mode of operation, and (b) a switching assembly opera ble to select one of the normal mode of operation and the safe mode of operation, the switching assembly comprising a first switch and a second switch adapted to operate synchro nously, wherein the first switch is adapted to selectively connect and disconnect the first pair of terminals, and wherein the second switch is adapted to selectively connect and disconnect the second pair of terminals. Furthermore, the control logic is adapted to generate the output signal indic ative of the normal mode of operation when both the first pair of terminals and the second pair of terminals are re spectively connected, and to generate the output signal in dicative of the safe mode of operation when at least one of the first pair of terminals and the second pair of terminals are not respectively connected.

This aspect of the invention is based on the idea that the output signal only indicates the normal mode of operation when both pairs of terminals are respectively connected, i.e. when the terminals of the first pair of terminals are con nected and the terminals of the second pair of terminals are connected. In all other situations, i.e. when only the termi nals of one of the (first and second) pairs of terminals are connected or when the terminals of neither the first nor the second pair of terminals are connected, the output signal will indicate the safe mode of operation. Thereby, even if an error or failure occurs in the switching assembly or in ca bles connecting the terminals and the switching assembly af ter the switching assembly has been operated to select the safe mode of operation, the output signal will still indicate the safe mode of operation.

In the present context, the term "a first switch and a second switch adapted to operate synchronously" may in particular denote that when the first switch is closed, also the second switch will be closed, and vice versa. In other words, the first and second switches are linked to always be in the same state (closed or open) .

According to an embodiment of the invention, the controller further comprises (a) a first signal generator connected to one of the first pair of terminals and adapted to generate a first characteristic signal, (b) a first signal detector con nected the other one of the first pair of terminals and adapted to detect the first characteristic signal, (c) a sec ond signal generator connected to one of the second pair of terminals and adapted to generate a second characteristic signal, and (d) a second signal detector connected to the other one of the second pair of terminals and adapted to de tect the second characteristic signal. Furthermore, the con trol logic is adapted to determine that the first pair of terminals are connected when the first signal detector de tects the first characteristic signal and determine that the second pair of terminals are connected when the second signal detector detects the second characteristic signal.

In this embodiment, the first signal generator generates a first characteristic signal and outputs it via one terminal of the first pair of terminals. The first signal detector is connected to the other terminal of the first pair of termi nals and capable of detecting the first characteristic sig nal. Only if the first signal detector detects the first characteristic signal, the control logic determines that the terminals of the first pair of terminals are connected. Simi larly, the second signal generator generates a second charac teristic signal and outputs it via one terminal of the second pair of terminals. The second signal detector is connected to the other terminal of the second pair of terminals and capa ble of detecting the second characteristic signal. Only if the second signal detector detects the second characteristic signal, the control logic determines that the terminals of the second pair of terminals are connected. By requiring that the first characteristic signal, which is output at one of the terminals of the first pair of termi nals, is also received at the other terminal of the first pair of terminals, and similarly that the second characteris tic signal, which is output at one of the terminals of the second pair of terminals, is also received at the other ter minal of the second pair of terminals, safety and robustness is further improved. In particular, a situation where some of the terminals of different pairs of terminals are connected due to an error, such as defective insulation material or an error in the switching assembly, will not lead to an output signal from the control logic indicating the safe mode of op eration .

According to a further embodiment of the invention, the first characteristic signal is a pulsed signal having a first fre quency and the second characteristic signal is a pulsed sig nal having a second frequency.

Pulsed signals are easy to generate and detect by standard electronic components and thus present a cheap and effective means of improving safety.

According to a further embodiment of the invention, the first frequency differs from the second frequency.

Alternatively or additionally, the first characteristic sig nal may also have a duty cycle which is different from the duty cycle of the second characteristic signal.

According to a further embodiment of the invention, the con troller is a safety PLC, i.e. a programmable logic controller dedicated to safety systems.

This embodiment is particularly advantageous in cases where the wind turbine already comprises a safety PLC, such that the present invention may be implemented by corresponding programming of the safety PLC. According to a further embodiment of the invention, the con trol logic comprises a first relay and a second relay ar ranged in series between a voltage source and an output ter minal, wherein the first relay is adapted to close and the second relay is adapted to close when the first pair of ter minals are connected and the second pair of terminals are connected .

When both relays are closed (corresponding to the normal mode of operation) , they will form a connection between the volt age source and the output terminal. In all other situations (i.e. one or two open relays, corresponding to the safe mode of operation) , the output terminal will not be connected to the voltage source. Thus, in this embodiment the output sig nal equals the voltage of the voltage source when indicating normal mode of operation.

According to a further embodiment of the invention, the first relay comprises a first auxiliary relay adapted to indicate the state of the first relay, the second relay comprises a second auxiliary relay adapted to indicate the state of the second relay, and the first auxiliary relay and the second auxiliary relay are connected in series to form a feedback circuit .

The auxiliary relays mirror the state of the respective relay and thereby the feedback circuit makes it possible for the controller to verify that the respective states of the relays correspond to the detections of respective connections be tween the terminals of the first and second pairs of termi nals. If the verification fails, e.g. if one of the first and second relays is unable to open, an error signal may be out put from the controller.

According to a second aspect of the invention, there is pro vided a wind turbine comprising (a) a wind turbine generator, (b) a wind turbine controller, and (c) a safety device ac- cording to the first aspect or any of the above embodiments, wherein the wind turbine is communicatively coupled to re ceive the output signal from the safety device and adapted to operate the wind turbine generator in either a safe mode of operation or a normal mode of operation in dependency of the output signal.

The wind turbine according to this aspect of the invention is based on and profits from the same idea as the first aspect of the invention, which has been discussed in detail above.

According to an embodiment of the invention, the wind turbine controller is responsive to local input only when operating in the safe mode of operation, and the wind turbine control ler is responsive to both local and remote input when operat ing in the normal mode of operation.

Thus, when operating in the safe mode of operation, the wind turbine controller does not respond to external input (such as set points or other commands from a central wind farm con troller) but can only be influenced by local input, in par ticular settings input by a technician during maintenance.

According to a third aspect of the invention, there is pro vided a wind farm comprising a plurality of wind turbine ac cording to the second aspect or any of the above embodiments.

According to a fourth aspect of the invention, there is pro vided a method of switching a wind turbine between a safe mode of operation and a normal mode of operation. The method comprises (a) determining whether a first pair of terminals are connected, (b) determining whether a second pair of ter minals are connected, (c) generating an output signal indica tive of the normal mode of operation when it is determined that both the first pair of terminals and the second pair of terminals are respectively connected, and (d) generating an output signal indicative of the safe mode of operation when it is determined that at least one of the first pair of ter- minals and the second pair of terminals are not respectively connected .

This aspect of the invention is based on the same idea as the first aspect described above.

According to a fifth aspect of the invention, there is pro vided a computer program comprising computer executable in structions which, when executed by a computer processing de vice, are adapted to perform the steps of the method accord ing to the fourth aspect.

It is noted that embodiments of the invention have been de scribed with reference to different subject matters. In par ticular, some embodiments have been described with reference to method type claims whereas other embodiments have been de scribed with reference to apparatus type claims. However, a person skilled in the art will gather from the above and the following description that, unless otherwise indicated, in addition to any combination of features belonging to one type of subject matter also any combination of features relating to different subject matters, in particular to combinations of features of the method type claims and features of the ap paratus type claims, is part of the disclosure of this docu ment .

The aspects defined above and further aspects of the present invention are apparent from the examples of embodiments to be described hereinafter and are explained with reference to the examples of embodiments. The invention will be described in more detail hereinafter with reference to examples of embodi ments. However, it is explicitly noted that the invention is not limited to the described exemplary embodiments. Brief Description of the Drawing

Figure 1 shows a safety device for switching a wind turbine between a safe mode of operation and a normal mode of opera tion in accordance with an embodiment of the present inven tion.

Figure 2 shows a safety device for switching a wind turbine between a safe mode of operation and a normal mode of opera tion in accordance with a further embodiment of the present invention .

Detailed Description

The illustration in the drawing is schematic. It is noted that in different figures, similar or identical elements are provided with the same reference numerals or with reference numerals which differ only within the first digit.

Figure 1 shows a safety device 100 for switching a wind tur bine between a safe mode of operation (i.e. a mode of opera tion where a technician can safely perform service and maintenance work on the wind turbine without the risk of the wind turbine suddenly changing its mode of operation in re sponse to an external control signal or message) and a normal mode of operation (i.e. a power producing mode) in accordance with an embodiment of the present invention. The safety de vice 100 comprises a controller 110 and a switching assembly 120.

The controller 110 is preferably implemented as a safety PLC (i.e. a programmable logic controller dedicated to safety systems) and comprises a first pair of terminals 111, 112, a second pair of terminals 113, 114, and control logic (not shown) for generating an output signal indicative of either the safe mode of operation or the normal mode of operation and supplying the output signal to output terminal 115. The switching assembly 120 is operable to select one of the normal mode and the safe mode of operation, i.e. the switch ing assembly can be operated by a technician when arriving at the wind turbine to initiate service or maintenance work or when leaving the wind turbine after having performed such work. The switching assembly 120 comprises a first switch 121 arranged to close or break an electrical connection between the terminals 111 and 112 of the first pair of terminals, and a second switch 122 arranged to close or break an electrical connection between the terminals 113 and 114 of the second pair of terminals. The first switch 121 and the second switch 122 are linked to operate synchronously in the sense that they are both either closes or open.

The control logic of the controller 110 is adapted to deter mine whether the terminals 111 and 112 of the first pair of terminals are connected or not and whether the terminals 113 and 114 of the second pair of terminals are connected or not. When the control logic determines that the terminals 111, 112 and 113, 114 of both pairs are respectively connected, it sets the output signal supplied to the output terminal 115 to indicate the normal mode of operation, e.g. by outputting a digital high value. On the other hand, when the control logic determines that the terminals of at least one of the pairs of terminals are not connected, i.e. when the terminals 111 and 112 are not connected and/or the terminals 113 and 114 are not connected, it sets the output signal supplied to the out put signal 115 to indicate the safe mode of operation, e.g. by outputting a digital low value. The output signal is sup plied from the output terminal 115 to a wind turbine control ler 130 which controls the mode of operation of a correspond ing wind turbine (not shown) .

The controller preferably comprises a first signal generator, a first signal detector, a second signal generator, and a second signal detector (not shown) . These signal generators and detectors are typically available on a safety PLC and therefore merely need to be set up. The first signal generator is adapted to generate a first characteristic signal, such as a pulsed signal with a prede termined first frequency and feed it to terminal 112. The first signal detector is coupled to the terminal 111 and adapted to detect the first characteristic signal in case this arrives at the terminal 111. Similarly, the second sig nal generator is adapted to generate a second characteristic signal, such as a pulsed signal with a predetermined second frequency and feed it to terminal 114. The second signal de tector is coupled to the terminal 113 and adapted to detect the second characteristic signal in case this arrives at the terminal 113. The pulsed signals may be square wave signals with 50:50 duty cycle. Alternatively, the first characteris tic signal may have a duty cycle that differs from the duty cycle of the second characteristic signal.

The control logic now determines that the terminals 111 and 112 of the first set of terminals are connected when the first signal detector detects the first characteristic sig nal. Similarly, the control logic determines that the termi nals 113 and 114 of the second pair of terminals are connect ed when the second signal detector detects the second charac teristic signal. In other words, a connection between termi nal 111 and both terminals 113 and 114 (e.g. due to an error in the switching assembly 120 or due to faulty isolation of the cables connecting the terminals 111, 112, 113, 114 and the switching assembly 120) will cause the control logic to determine that the terminals 111 and 112 are connected and that the terminals 113 and 114 are not connected.

One of the strengths of the safety device 100 is that it only outputs the output signal indicating the normal mode of oper ation when both switches 121 and 122 are closed and all parts of the device are operating correctly. If one of the switches 121, 122 or one or more of the signal generators and detec tors of the controller 110 malfunctions, it will automatical ly result in an output signal indicating the safe mode of op- eration. Thus, if such malfunction occurs while the techni cian is working on the wind turbine, the wind turbine will continue operating in the safe mode of operation.

Figure 2 shows a safety device 200 for switching a wind tur bine between a safe mode of operation and a normal mode of operation in accordance with a further embodiment of the pre sent invention. More specifically, the controller 210 in this embodiment is not a readily available safety PLC but a dedi cated electronic unit designed to perform the same functions as discussed above in conjunction with Figure 1. That is, the controller 210 comprises a first signal generator coupled to terminal 212, a first signal detector coupled to terminal 211, a second signal detector coupled to terminal 214, and a second signal detector coupled to terminal 213. The switching assembly 220 is similar to the switching assembly 120 de scribed above in conjunction with Figure 1.

In this embodiment, the control logic is constituted by a first relay 216 and a second relay 217 arranged in series be tween a voltage source (providing a voltage corresponding to a digital high value) within the controller 210 and output terminal 215 such that when both relays 216 and 217 are closed, the voltage at the output terminal corresponds to that of the voltage source. When the first signal detector detects the first characteristic signal at terminal 211 and the second signal detector detects the second characteristic signal at terminal 213, the first relay 216 is closed and the second relay 217 is closed.

A further feature of this embodiment is that the first relay 216 comprises a first auxiliary relay 216a and the second re lay comprises a second auxiliary relay 217a. The first auxil iary relay mirrors the actual state (opened or closed) of the first relay 216 and the second auxiliary relay 217a mirrors the actual state of the second auxiliary relay 217. The aux iliary relays are arranged in series to form feedback loop 218 which allows the controller 210 to monitor whether the actual state of the relays 216 and 217 corresponds to the de sired state, i.e. to the detection results of the first and second signal detectors. If this is not the case, the con troller 210 outputs a corresponding error signal (not shown) indicating that one of the relays 216 and 217 is defective.

Due to the absence of a safety PLC, the present embodiment requires some dedicated hardware and corresponding physical installation of the same. However, neither the cost nor the effort is high in consideration of the obtained benefits of being able to safely switch a wind turbine into the safe mode of operation during maintenance and repair work.

It is noted that the term "comprising" does not exclude other elements or steps and the use of the articles "a" or "an" does not exclude a plurality. Also elements described in as sociation with different embodiments may be combined. It is further noted that reference signs in the claims are not to be construed as limiting the scope of the claims.