T 2711/18 17-11-2022

1. The appeal is admissible.

2. Main request - Novelty (Article 100(a) EPC in connection with Article 54 EPC)

2.1 Novelty in view of document D1

2.1.1 The subject-matter of claim 1 of the main request is new in view of document D1.

2.1.2 Document D1 does not disclose the feature of claim 1 of defining the voltage bounding range based on the electrical characteristic of the transmission line.

In particular, document D1 on page 8, line 30 to page 9, line 10, which the respondent primarily relied on, discloses a voltage limiter for the wind turbine reference voltage. This passage indicates that the voltage limiter serves to take account of different transmission conditions with respect to different wind turbines. However, it does not directly and unambiguously disclose that a voltage bounding range is in fact based on the different conditions and, in particular, on an electrical characteristic of the transmission line.

2.1.3 The respondent argued in favour of a broad interpretation of claim 1, in the sense that the formulation "based on" was to be interpreted as including any kind of relationship between the voltage bounding range and the electrical characteristic of the transmission line.

2.1.4 However, the board is not convinced that claim 1 is susceptible to such an unreasonably broad interpretation. Rather, it is clear from the wording of claim 1 alone that "based on" is intended to express and be understood by the skilled person as a factual reflection of an electric characteristic of the transmission line in the definition of the voltage bounding range. However, this does not result from document D1.

2.1.5 The board therefore arrived at the conclusion that the subject-matter of claim 1 of the main request is new in view of document D1. The same applies to the subject-matter of independent claim 14 of the main request.

2.2 Novelty in view of document D9

2.2.1 The subject-matter of claim 1 of the main request is not new in view of document D9.

2.2.2 It was in dispute between the parties whether document D9 discloses obtaining information regarding an electrical characteristic of a transmission line connecting the wind turbine output terminal to a point of common coupling to which plural other wind turbines are connectable and defining the voltage bounding range based on the electrical characteristic of the transmission line.

2.2.3 The board does not agree with the appellant that claim 1 or the related description in the patent implies the necessity of measurements at at least two different locations on a transmission line in order to obtain an electric characteristic of the transmission line in the sense of claim 1.

The board rather concurs with the respondent that it is possible to obtain information regarding an electrical characteristic of the transmission line by measuring the voltage at the end of the transmission line, i.e. at the POCC.

More specifically, claim 11 of the patent may refer to "measuring the characteristic of the transmission line, in particular regarding possible voltages at the transmission line" (emphasis added), i.e. to a plurality of voltages. Accordingly, the description of the patent in paragraph [0014] refers to "electrical measurements" (emphasis added).

However, the board does not consider this disclosure to imply directly and unambiguously that more than one measurement on the transmission line is necessary to obtain information regarding an electrical characteristic of the transmission line. It is further to be noted that, as was pointed out by the respondent, claim 1 does not provide any definition of the electrical characteristic of the transmission line.

2.2.4 Nor is it derivable from the disclosure in paragraph [0041] of the patent that a plurality of measurements is required to obtain information about an electrical characteristic of the transmission line within the meaning of claim 1.

While the first sentence of this paragraph refers to possible voltages in accordance with claim 11 of the patent, the next sentence specifies that "the voltage" can be measured at the point of common coupling. The next sentence discloses that "the voltage" may be measured at the wind turbine output terminal. The following sentence then states that such electrical quantities may be measured at plural different locations along the transmission line between wind turbine and POCC. In the light of this description, the board considers that measuring a plurality of voltages at different locations merely constitutes a specific embodiment of the subject-matter of claim 1.

The board therefore agrees with the respondent that a plausible understanding of the wording "possible voltages" (emphasis added) includes a plurality of measurements at the same location at different points in time and not necessarily measurements at different locations. Thus, paragraph [0041] in principal reveals different possibilities to obtain an electrical characteristic of the transmission line:

(1) by measuring at the POCC

(2) by measuring at the wind turbine output terminal

(3) by combining measurements according to (1) and (2)

Therefore, in line with the disclosure of the patent in paragraph [0041], voltage measurements (only) at the POCC to which the wind turbine output terminal is connected via the transmission line, can be considered to correspond to information regarding an electrical characteristic of the transmission line within the meaning of claim 1.

2.2.5 In document D9, the POCC is connected to a wind turbine via a transmission line. Document D9 further discloses measuring a voltage Umeas at the POCC. The measured voltage Umeas is applied as an input signal to a controller (see paragraph [0067], figure 1). For the sake of completeness, it is noted that a plurality of measurements, corresponding to the plural wording "voltages" used in the patent, are thereby performed.

As is further disclosed in D9, see e.g. paragraphs [0008], [0067] and [0068] as well as figures 1 to 3, the voltage bounding range, defined by the upper and lower limit voltages Umaxref and Uminref, is clearly based on the voltage Umeas measured at the POCC. The voltage bounding range in D9 is thus based on the electrical characteristic of the transmission line as recited in claim 1.

2.2.6 The board thus concluded that the subject-matter of claim 1 of the main request is not new in view of document D9. Consequently, the ground for opposition under Article 100(a) EPC in combination with Article 54 EPC prejudices the maintenance of the patent as granted.

3. First auxiliary request

3.1 Amendments (Article 123(2) EPC)

3.1.1 The subject-matter of claim 1 does not extend beyond the content of the application as originally filed.

3.1.2 Claim 1 of the first auxiliary request includes the additional features of claim 4, which originally depended on claim 2. Claim 2 as filed recites that the voltage bounding range is defined to be a voltage range between maximum voltage Vmax and minimum voltage Vmin.

3.1.3 The board agrees with the appellant that the definition of claim 2 is already implied in the wording "voltage bounding range". In particular, there cannot be any doubt that the skilled person would understand from the respective wording in the overall context of claim 1 that a voltage range requires an upper voltage limit and lower voltage limit.

3.1.4 Correspondingly, the board does not agree with the respondent that claim 1, without the definition of claim 2, may comprise a voltage bounding range, which is open, i.e. unlimited at one end.

3.1.5 The omission of the feature of original claim 2 therefore does not result in an inadmissible extension of the subject-matter of claim 1. The subject-matter of claim 1 of the first auxiliary request therefore meets the requirement of Article 123(2) EPC. The same applies to the subject-matter of independent claim 13 of the first auxiliary request.

3.2 Sufficiency of disclosure (Article 83 EPC)

3.2.1 The patent describes the invention as defined in claims 1 and 13 in a manner sufficiently clear and complete for it to be carried out by the person skilled in the art.

3.2.2 As regards the first objection raised by the respondent under Article 83 EPC against the first auxiliary request, the board concurs with the appellant that the skilled person would know how to calculate the voltage Vturb, i.e. the output voltage of the turbine, off-line (prior to the operation of the wind turbine) by means of the equation in paragraph [0056] of the patent. In particular, the appellant convincingly argued that the skilled person can, for example, use an average expected wind speed to calculate the actual possible maximum or minimum voltage expected from the wind turbine if the actual wind speed was not known.

The board therefore considers the description in paragraphs [0056] and [0062] not to prevent the skilled person from implementing the invention.

3.2.3 The respondent raised a second objection under Article 83 EPC against claim 12 of the first auxiliary request (corresponding to claim 13 as granted). In this respect, the board agrees with the appellant that the person skilled in the art would know that the voltage bounding range may be maintained constant after it has been defined according to the subject-matter of granted claim 1. The invention as defined in claim 12 is therefore sufficiently described for it to be carried out by the skilled person.

3.2.4 The respondent raised a third objection under Article 83 EPC in view of the description in paragraph [0014] of the patent, which allegedly implied that current measurements could be performed without voltage measurements. In this respect, the board agrees with the appellant that the skilled person would not understand paragraph [0014] of the patent to imply that only current measurements are comprised in the information regarding an electrical characteristic of the transmission line. Rather, the skilled person would clearly understand that further information may be comprised in the information regarding the electrical characteristic of the transmission line. The description in paragraph [0014] therefore does not hinder the skilled person from implementing the invention of claims 1 and 13.

3.2.5 A fourth objection under Article 83 EPC, raised by the respondent, concerned claim 7 of the first auxiliary request (corresponding to claim 8 as granted). The board in this context agrees with the appellant that the skilled person in the technical field of wind turbine control is well aware of the necessary tools and skills to simulate electrical circuits in this context. The skilled person therefore would have no difficulties in carrying out the invention as defined in claim 7.

3.3 Novelty in view of document D1 (Article 54 EPC)

3.3.1 The conclusions on novelty of the subject-matter of claim 1 of the main request in view of document D1 likewise apply to the subject-matter of claim 1 of the first auxiliary request, see point 2.1 above.

3.3.2 In particular, document D1 does not disclose defining a voltage bounding range based on an electrical characteristic of the transmission line. It follows from this that document D1 does not disclose the additional feature of claim 1 of the first auxiliary request, namely that the electrical characteristic comprises a transformation ratio of a wind turbine transformer connected between the wind turbine output terminal and the point of common coupling, the transformation ratio being a ratio between a voltage at a medium voltage side and a voltage at a low voltage side of the wind turbine transformer, wherein the wind turbine output terminal is connected to the low voltage side of the wind turbine transformer.

3.3.3 The board has therefore come to the conclusion that the subject-matter of claim 1 of the first auxiliary request is new in view of document D1, Article 54 EPC.

3.4 Inventive step in view of document D1 (Article 56 EPC)

Document D1 in combination with the common general knowledge of the skilled person

3.4.1 The subject-matter of claim 1 of the first axillary request is not rendered obvious by a combination of document D1 with the common general knowledge of the skilled person.

3.4.2 In the decision under appeal, the opposition division found that the skilled person would obviously take the transformation ratio of the transformer in the transmission line together with the electrical characteristic of the transmission line into consideration, when defining the limit to be set in the limiter 182. Since document D1 disclosed a transformer and a limiter, the skilled person would see the relation between these two elements.

3.4.3 The board is not convinced by this reasoning. In particular, the board does not recognise any corresponding relation in document D1 between the limiter on the one side and the transformer being arranged in the transmission line on the other side.

3.4.4 The respondent cited document D1 on page 6, line 31 to page 7, line 1, where it is generally disclosed that the intermediate transformer can be taken into account in a compensation unit for calculating the wind turbine reference voltage. Furthermore, the respondent's submission focuses on page 8, line 30 to page 9, line 10 of D1, where it is disclosed that a limiter is provided to prevent damage caused by excessive reference voltages due to long transmission lines and corresponding complex impedances.

3.4.5 However, the board agrees with the appellant that document D1 in the respective passages does not disclose directly and unambiguously a transformation ratio that is considered in the compensation unit. In particular, the passage on page 6, line 31 to page 7, line 1 is exclusively concerned with the compensation unit and a calculation of the reference voltage which takes into account influences of the transmission line and/or an intermediate transformer. Document D1, however, does not disclose any details of how the intermediate transformer is considered in the calculation of the reference voltage. Nor is there any relation apparent between calculating the (individual) reference voltages and determining the voltage limits by means of the limiter.

3.4.6 Consequently, the board considers that document D1 does not disclose or suggest taking into account the transformation ratio of the intermediate transformer, and in particular not taking into account the transformation ratio for obtaining information regarding an electrical characteristic of the transmission line in the sense of claim 1 of the first auxiliary request.

Furthermore, the board does not understand this to correspond to normal practice which the person skilled in the art would, without any motivation or hint in this respect, implement in D1. The respondent has not submitted anything further in this regard.

3.4.7 Therefore, the board concluded that the subject-matter of claim 1 of the first auxiliary request is not rendered obvious by document D1 in combination with the common general knowledge of the skilled person.

Document D1 in combination with document D2

3.4.8 The subject-matter of claim 1 of the first auxiliary request is also not rendered obvious by a combination of documents D1 and D2.

3.4.9 As outlined in particular under the points 3.4.4 to 3.4.6 above, document D1 merely generally discloses that an intermediate transformer is somehow considered in the calculation of the wind turbine reference voltage. Document D1 does not directly and unambiguously, either explicitly or implicitly, disclose that it is the transformation ratio of the intermediate transformer that is considered in the calculation of the wind turbine reference voltage.

The respondent's argument with regard to a combination of documents D1 and D2 is based on the assumption that document D1 discloses a transformation ratio of an intermediate transformer, on which the calculation of the reference voltage is based. According to the respondent, when transferring the teaching from document D2 to document D1, the error variable e(z) in the equations on page 2 of D2 would be based on the transformation ratio of an intermediate transformer.

However, since the board is convinced that, as outlined above, document D1 does not directly and unambiguously disclose the use of the transformation ratio of an intermediate transformer as part of such a calculation, the combination of documents D1 and D2 in any case does not result in the subject-matter of claim 1 of the first auxiliary request.

This statement applies regardless of further questions that were assessed in this context, in particular the questions of how the objective technical problem should be formulated as well as the question of whether the skilled person would have considered document D2 at all.

3.4.10 In conclusion, the subject-matter of claim 1 of the first auxiliary request is not rendered obvious by a combination of documents D1 and D2. The same applies to the subject-matter of independent claim 13 of the first auxiliary request.

Given that the respondent did not raise any further objections under Article 56 EPC against the first auxiliary request, the subject-matter of claims 1 and 13 of this request is considered to involve an inventive step under Article 56 EPC.

4. Result

Given that the maintenance of the patent as granted is prejudiced by the ground for opposition under Article 100(a) in combination with Article 54 EPC, but none of the objections raised by the respondent prejudices the maintenance of the first auxiliary request, the board had to accede to the appellant's first auxiliary request.