Office Action 1: Non-Final Rejection (2024-09-19)
Rejection types: 102 - Lack of Novelty, 103 - Obviousness

CLAIMS:
CLAIMS:

1\. A converter station (10), for a bipole power transmission scheme, comprising:
a first voltage source converter (12) having a first terminal (14) for connection
to a first transmission conduit, a second terminal (16) for connection to a return conduit, and at least one converter limb (18A, 18B, 18C) extending between the first and second terminals (14, 16), the or each converter limb (18A, 18B, 18C) including first and second limb portions (20A, 20B, 20C, 22A, 22B, 22C) separated by a corresponding first AC terminal (24A, 24B, 24C) for connection to a respective phase (A, B, C) of a first AC network, the or each first limb portion (20A, 20B, 20C) including a first chain-link converter (26) extending between the associated first AC terminal (24A, 24B, 24C) and the first terminal (14), the or each second limb portion (22A, 22B, 22C) including a second chain-link converter (28) extending between the associated first AC terminal (24A, 24B, 24C) and the second terminal (16), and each chain-link converter (26, 28) including a plurality of series connected chain-link modules (30) each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter (26, 28) is controllable to provide a stepped variable voltage source; and
a second voltage source converter (32) having a third terminal (34) for
connection to a second transmission conduit, a fourth terminal (36) for connection to the return conduit, and at least one converter limb (18A, 18B, 18C) extending between the third and fourth terminals (34, 36), the or each converter limb (18A, 18B, 18C) including third and fourth limb portions (38A, 38B, 38C, 40A, 40B, 40C) separated by a corresponding second AC terminal (42A, 42B, 42C) for connection to a respective phase (A, B, C) of a second AC network, the or each third limb portion (38A, 38B, 38C) including a third chain-link converter (44) extending between the associated second AC terminal (42A, 42B, 42C) and the third terminal (34), the or each fourth limb portion (40A, 40B, 40C) including a fourth chain-link converter (46) extending between the associated second AC terminal (42A, 42B, 42C) and the fourth terminal (36), and each chain-link converter (44, 46) including a plurality of series connected chain-link modules (30) each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter (44, 46) is controllable to provide a stepped variable voltage source, each of the second and third chain-link converters (28, 44) including a first number (58) of series-connected chain-link modules (30), and each of the first and fourth chain-link converters (26, 46) including a second number (52) of series- connected chain-link modules (30), the second number (52) being greater than the first number (58).

2\. A converter station (10) according to Claim 1 wherein each of the second and third chain-link converters (28, 44) include the same first number (58) of series- connected chain-link modules (30).

3\. A converter station (10) according to Claim 1 or Claim 2 wherein each of the first and fourth chain-link converters (26, 46) include the same second number (52) of series-connected chain-link modules (30).

4\. A converter station (10) according to any preceding claim wherein each chain- link module (30) has the same topology.

5\. A converter station (10) according to Claim 4 wherein each chain-link module (30) includes a first pair of switching elements connected in parallel with the energy storage device in a half-bridge arrangement to define a 2-quadrant unipolar module.

6\. A converter station (10) according to any preceding claim wherein at least one voltage source converter (12, 32) includes a corresponding voltage source converter controller (48, 50) programmed to control the stepped variable voltage source provided by the said corresponding voltage source converter (12, 32), and when doing so to balance the total energy stored by the energy storage devices (30) in one limb portion (20A, 20B, 20C, 40A, 40B, 40C) of the said voltage source converter (12, 32) with the total energy stored by the energy storage devices (30) in the other corresponding limb portion (22A, 22B, 22C, 38A, 38B, 38C) of the voltage source converter (12, 32).

7\. A converter station (10) according to Claim 6 wherein the at least one voltage source converter controller (48, 50) is programmed to cause the chain-link modules (50) in the limb portion (20A, 20B, 20C, 40A, 40B, 40C) having the higher second number (52) of chain-link modules (30) to store a proportionally lower individual average amount of energy (54) than the individual average amount of energy (56) stored by each of the chain-link modules (30) in the other corresponding limb portion (22A, 22B, 22C, 38A, 38B, 38C).

8\. A method of operating a converter station (10) comprising: a first voltage source converter (12) having a first terminal (14) for connection to a first transmission conduit, a second terminal (16) for connection to a return conduit, and at least one converter limb (18A, 18B, 18C) extending between the first and second terminals (14, 16), the or each converter limb (18A, 18B, 18C) including first and second limb portions (20A, 20B, 20C, 22A, 22B, 22C) separated by a corresponding first AC terminal (24A, 24B, 24C) for connection to a respective phase (A, B, c) of a first AC network, the or each first limb portion (20A, 20B, 20C) including a first chain-link converter (26) extending between the associated first AC terminal (24A, 24B, 24C) and the first terminal (14), the or each second limb portion (22A, 22B, 22C) including a second chain-link converter (28) extending between the associated first AC terminal (24A, 24B, 24C) and the second terminal (16), and each chain-link converter (26, 28) including a plurality of series connected chain-link modules (30) each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter (26, 28) is controllable to provide a stepped variable voltage source; and
a second voltage source converter (32) having a third terminal (34) for connection to a second transmission conduit, a fourth terminal (36) for connection to the return conduit, and at least one converter limb (18A, 18B, 18C) extending between
the third and fourth terminals (34, 36), the or each converter limb (18A, 18B, 18C) including third and fourth limb portions (38A, 38B, 38C, 40A, 40B, 40C) separated by a corresponding second AC terminal (42A, 42B, 42C) for connection to a respective phase (A, B, C) of a second AC network, the third limb portion (38A, 38B, 38C) including a third chain-link converter (44) extending between the associated second AC terminal (42A, 42B, 42C) and the third terminal (34), the fourth limb portion (40A, 40B, 40C) including a fourth chain-link converter (46) extending between the associated second AC terminal (42A, 42B, 42C) and the fourth terminal (36), and each chain-link converter (44, 46) including a plurality of series connected chain-link modules (30) each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter (44, 46) is controllable to provide a stepped variable voltage source, the method comprising the steps of:
providing each of the second and third chain-link converters (28, 44) with a first number (58) of series-connected chain-link modules (30); and
providing each of the first and fourth chain-link converters (26, 46) with a second number (52) of series-connected chain-link modules (30), the second number (52) being greater than the first number (58). 11 12 13 5 10 15 20 25 30 35

OFFICE ACTION:
DETAILED ACTION
This Office action is in response to the national stage application filed on 06 January 2023.
Notice of Pre-AIA  or AIA  Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
In the event the determination of the status of the application as subject to AIA  35 U.S.C. 102 and 103 (or as subject to pre-AIA  35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA  to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
This application currently names joint inventors. In considering patentability of the claims the examiner presumes that the subject matter of the various claims was commonly owned as of the effective filing date of the claimed invention(s) absent any evidence to the contrary.  Applicant is advised of the obligation under 37 CFR 1.56 to point out the inventor and effective filing dates of each claim that was not commonly owned as of the effective filing date of the later invention in order for the examiner to consider the applicability of 35 U.S.C. 102(b)(2)(C) for any potential 35 U.S.C. 102(a)(2) prior art against the later invention.
Priority
Receipt is acknowledged of certified copies of papers required by 37 CFR 1.55.
Drawings
The drawings are objected to under 37 CFR 1.83(a) because they fail to show the plurality of series connected chain-link modules that are included within each of the first through fourth chain-link converters as described in the specification. More particularly, the drawings also fail to show, “each of the second and third chain-link converters including a first number of series-connected chain-link modules, and each of the first and fourth chain-link converters including a second number of series-connected chain-link modules, the second number being greater than the first number” as described and claimed.
Any structural detail that is essential for a proper understanding of the disclosed invention should be shown in the drawing. In addition, the drawings must show every feature of the invention specified in the claims. MPEP § 608.02(d). Corrected drawing sheets in compliance with 37 CFR 1.121(d) are required in reply to the Office action to avoid abandonment of the application. Any amended replacement drawing sheet should include all of the figures appearing on the immediate prior version of the sheet, even if only one figure is being amended. The figure or figure number of an amended drawing should not be labeled as “amended.” If a drawing figure is to be canceled, the appropriate figure must be removed from the replacement sheet, and where necessary, the remaining figures must be renumbered and appropriate changes made to the brief description of the several views of the drawings for consistency. Additional replacement sheets may be necessary to show the renumbering of the remaining figures. Each drawing sheet submitted after the filing date of an application must be labeled in the top margin as either “Replacement Sheet” or “New Sheet” pursuant to 37 CFR 1.121(d). If the changes are not accepted by the examiner, the applicant will be notified and informed of any required corrective action in the next Office action. The objection to the drawings will not be held in abeyance.
Claim Interpretation
It is noted that the use of the term, “including” in the claims is interpreted synonymously with “comprising”, in that it indicates an open-ended construction of a claim limitation in which it is used. See MPEP 2111.03 subsect. I.
This is most notable in regards to the recitation, “each of the second and third chain-link converters including a first number of series-connected chain-link modules, and each of the first and fourth chain-link converters including a second number of series-connected chain-link modules” in claim 9 and to the similar, corresponding limitations recited in claim 16. That is, in construing the claim scope and applying prior art, it is recognized that the second and third chain-link converters may include further series-connected chain-link modules in addition to the first number, and likewise that the first and fourth chain-link converters may include further series-connected chain-link modules in addition to the second number.
Claim Objections
Claim 14 is objected to because of the following informalities:
In claim 14, “at least one voltage source converter” should be changed to, “at least one of the first and second voltage source converters” or a similar construction, in order to indicate the proper antecedent basis of the terminology. Appropriate correction is required.
Claim Rejections - 35 USC § 102
The following is a quotation of the appropriate paragraphs of 35 U.S.C. 102 that form the basis for the rejections under this section made in this Office action:
A person shall be entitled to a patent unless –
(a)(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention.
(a)(2) the claimed invention was described in a patent issued under section 151, or in an application for patent published or deemed published under section 122(b), in which the patent or application, as the case may be, names another inventor and was effectively filed before the effective filing date of the claimed invention.
Claims 9-13 and 16 are rejected under 35 U.S.C. 102(a)(1) and 102(a)(2) as being anticipated by WO 2019/161907 A1 to ABB SCHWEIZ AG (hereinafter “ABB”).
In re claim 9, ABB discloses a converter station for a bipole power transmission scheme (Figs. 8-9; p. 9, l. 9-24), comprising:
a first voltage source converter (801) having a first terminal (see annotated version of Fig. 9 of ABB, below) for connection to a first transmission conduit (832), a second terminal (see annotated figure) for connection to a return conduit (connection between the VSCs 801 and 802; see p. 9, l. 8-15 and p. 14, l. 23-31), and at least one converter limb (Fig. 9: converter limb connected to AC terminal 872) extending between the first and second terminals (see annotated figure), the or each converter limb including first and second limb portions (reactors and sub-module chains on either side of AC terminal 872) separated by a corresponding first AC terminal (872) for connection to a respective phase of a first AC network (860a),
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the or each first limb portion including a first chain-link converter (see annotated figure) extending between the associated first AC terminal (872) and the first terminal (see annotated figure),
the or each second limb portion including a second chain-link converter (see annotated figure) extending between the associated first AC terminal (872) and the second terminal (see annotated figure), and
each chain-link converter including a plurality of series connected chain-link modules (see annotated figure) each having a plurality of switching elements connected in parallel with an energy storage device (see example sub-modules/modules as shown in Figs. 1-3) whereby each chain-link converter is controllable to provide a stepped variable voltage source (p. 1, l. 17 – p. 2, l. 12); and
a second voltage source converter (Figs. 8, 9: 802; see the annotated Fig. 9 provided above; in addition, the citations/explanations provided above for the first VSC 801 apply, mutatis mutandis, to the second VSC 802, therefore the citations will not be repeated) having a third terminal for connection to a second transmission conduit, a fourth terminal for connection to the return conduit, and at least one converter limb extending between the third and fourth terminals, the or each converter limb including third and fourth limb portions separated by a corresponding second AC terminal for connection to a respective phase of a second AC network, the or each third limb portion including a third chain-link converter extending between the associated second AC terminal and the third terminal, the or each fourth limb portion including a fourth chain-link converter extending between the associated second AC terminal and the fourth terminal, and each chain-link converter including a plurality of series connected chain-link modules each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter is controllable to provide a stepped variable voltage source,
each of the second and third chain-link converters (see annotated figure, above) including a first number of series-connected chain-link modules (in the simplest case shown in Fig. 9, the first number may equal one; but see also p. 16, l. 11-20 and p. 25, l. 1-4: in other cases having more sub-modules in each converter, the first number may equal any other number that is less than the total number of sub-modules connected in the respective chain-link converter), and
each of the first and fourth chain-link converters (see annotated figure) including a second number of series-connected chain-link modules (in the simplest case, the second number is equal to two; or in other cases with more sub-modules than are shown in Fig. 9, the second number may be equal to the total number of sub-modules in a respective chain-link converter),
the second number being greater than the first number (in all cases as described above – i.e., 2>1, and the total number of sub-modules in either the first or fourth chain-link converter is greater than a number less than said total).
In re claim 16, the method of operation, as claimed, is largely directed to defining the structure of the converter station, the limitations of which are essentially identical to those of the apparatus of claim 9. Whereas the actual steps of the method itself constitute a rephrasing of the structural limitations found at the end of claim 9 regarding the number of chain-link modules in the first through fourth chain-link converters. Therefore, since ABB anticipates the converter station of claim 9 as explained above, ABB also inherently anticipates the method of operating the converter station as recited in claim 16, and the detailed citations and explanations will not be repeated.
In re claims 10-12, ABB discloses wherein each of the second and third chain-link converters include the same first number of series-connected chain-link modules (see annotated Fig. 9 of ABB, above – e.g., the second and third converters each include one module); wherein each of the first and fourth chain-link converters (see annotated figure) include the same second number of series-connected chain-link modules (e.g., they each include two modules as shown); and wherein each chain-link module has the same topology (see, e.g., p. 3, l. 27-32: in embodiments having larger numbers of sub-modules in each limb portion, it is sufficient to consider only the HB modules or only the FB modules as corresponding to the chain-link modules of the claimed invention).
In re claim 13, ABB discloses wherein each chain-link module (in the case of only considering HB modules/sub-modules as explained above from claim 12; see Fig. 2) includes a first pair of switching elements (IGBTs in Fig. 2) connected in parallel with the energy storage device (204) in a half-bridge arrangement to define a 2-quadrant unipolar module (Fig. 2).
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
Claim 14 is rejected under 35 U.S.C. 103 as being unpatentable over ABB, as cited above, in view of Cross et al. (US 2013/0182467; hereinafter “Cross”).
In re claim 14, ABB discloses the invention according to claim 9 as explained above, and further discloses wherein at least one voltage source converter includes a corresponding voltage source converter controller (p. 11, l. 26-33) programmed to control the stepped variable voltage source provided by the said corresponding voltage source converter (id.).
ABB does not disclose that the controller is programmed to balance the total energy stored by the energy storage devices in one limb portion of the said voltage source converter with the total energy stored by the energy storage devices in the other corresponding limb portion of the voltage source converter.
Whereas Cross discloses a chain-link converter (Figs. 1B, 2) and associated controller and method in which the voltage and consequently, the energy, stored in each of the individual chain-link module capacitors (i.e., energy storage devices) are balanced ([0086], [0093]-[0094]). As a result, the total energy stored by the modules in each of the limb portions will likewise be balanced. The balancing control is performed in order to reduce or eliminate DC voltage variations or oscillations for improved operation in an HVDC system ([0011]).
Therefore it would have been obvious to a person of ordinary skill in the art before the effective filing date of the claimed invention to have modified the converter station of ABB such that the controller is programmed to balance the total energy stored by the energy storage devices in one limb portion of the said voltage source converter with the total energy stored by the energy storage devices in the other corresponding limb portion of the voltage source converter as taught by Cross, for the purpose of improving performance of the HVDC transmission system by reducing or eliminating DC voltage variations or oscillations.
Allowable Subject Matter
Claim 15 is objected to as being dependent upon a rejected base claim, but would be allowable if rewritten in independent form including all of the limitations of the base claim and any intervening claims.
The following is a statement of reasons for the indication of allowable subject matter:
With respect to claim 15, the prior art made of record fails to disclose or suggest the invention according to claim 14 together with the additional features in which the controller is programmed to cause the chain-link modules in the limb portion having the higher second number of chain-link modules to store a proportionally lower individual average amount of energy than the individual average amount of energy stored by each of the chain-link modules in the other corresponding limb portion.
That is, the features recited in claim 15 are specific to the disclosed structural feature in which each of the first and fourth chain-link converters consist of more chain-link modules than the second and third chain-link converters. Therefore, it would not have been obvious to modify any of the known, prior art converter stations to be controlled in this manner.
Conclusion
The prior art made of record and not relied upon is considered pertinent to applicant's disclosure, as showing relevant examples of bipole HVDC converter stations with chain-link or other modular converters.

APPLICANT REBUTTAL: AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
REMARKS
Claims 9-16 are pending with claims 9 and 16 being independent claims. Claims 9-14 and 16 stand rejected. Claim 15 was objected to.
Objection to the Drawings:
The drawings were objected to under 37 CFR 1.83(a). As an initial matter, the Regulations state that drawings are required in a patent application
"where necessary
for the understanding of the subject matter sought to be patented," and that "[d]rawings
ma
y
include illustrations which
facilitate an understanding
of the invention." See 37 C.F.R. 1.81(a)-(b). Accordingly, a patent application is not required to show every detail of every possible embodiment of an invention in the drawings where a person having ordinary skill in the art would understand the subject matter sought to be patented in view of the drawings provided and corresponding portions of the specification. In this case, one of ordinary skill in the art can clearly understand the relationship between the chain-link converts.
Nonetheless, the Application asserts that the claim elements in question are adequately shown in Fig. 1 in the context of the following:
wherein each of the second and third chain-link converters (28, 44) includes a first number (58) of series-connected chain-link modules (30), and each of the first and fourth chain-link converters (26, 46) includes a second number (52) of series- connected chain-link modules (30), the second number (52) being greater than the
first number (58).
Objection to the Claims:
Claim 14 is objected to because of alleged minor informalities. The Applicant has revised the claim as requested.
AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
35 U.S.C. § 102:
Claims 9-13 and 16 were rejected under 35 U.S.C. § 102(a)(1) as being anticipated by WO 2019/161907 to ABB Schweiz AG et al. (ABB). The Applicant respectfully submits that the amendments made herein overcome the rejections.
ABB discloses a converter station (900) with first and second voltage source converters (801, 802) and teaches that:
(i)  a second (lower) chain-link converter (300) in the first voltage source converter
(801) and a third (upper) chain-link converter (300) in the second voltage source converter (802) have a first number of series-connected chain- link modules
(305, 310); and
(ii) a first (upper) chain-link converter (300) in the first voltage source converter
(801) and a fourth (lower) chain-link converter (300) in the second voltage source converter (802) have a second number of series-connected chain-link
modules (305, 310).
Although it may be accepted that the respective second and third, and first and fourth chain- link converters (300) in ABB arrangement have a number of chain-link modules, there is nothing in ABB to indicate or suggest that the second and third chain-link converters (300) should have fewer chain-link modules (305, 310) than the first and fourth chain-link converters (300).
In that regard, the text at lines 26 to 29 of page 24 of ABB mentions that Figure 9 shows a particular example in which each valve arm, i.e., each chain-link converter, of the converters (801, 802) includes one FB (full bridge) cell (305), i.e., one full bridge chain- link module, and
AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
one HB (half-bridge) cell (310), i.e., one half-bridge chain-link module, and that these valve arms are similar to those shown in Figure 5 of ABB.
With respect to Figure 5, the accompanying text at lines 11 to 20 of page 16 merely indicates that each valve arm, i.e., each chain-link converter, may include a mix of FB cells and HB cells, and that the number of HB cells and the number of FB cells in one valve arm may not be the same. By way of example, the text goes on to set out that a converter may include valve arms [plural], wherein a valve arm is a MMC (i.e., a chain-link converter) with 25% of FB submodules and 75% of HB submodules.
Meanwhile, the invention as claimed does not make such a distinction between chain-link modules, and merely requires a chain-link module to have a plurality of switching elements connected in parallel with an energy storage device (whereby the associated chain-link converter is controllable to provide a stepped variable voltage source). It follows that any module having those characteristics, i.e., both of the FB and HB modules disclosed in ABB, constitutes a chain- link module according to the invention. Therefore, in terms of disclosing the inclusion of chain- link modules within a respective chain-link converter (i.e., irrespective of the exact nature of those modules, be that full bridge or half- bridge), ABB provides no indication whatsoever that one chain-link converter should have a different number of such chain-link modules than any other chain-link converter.
In contrast, claim 9 requires the provision of each of the second and third chain-link converters including a first number of series-connected chain-link modules, and each of the first and fourth chain-link converters including a second number of series-connected chain-link modules, the second number being greater than the first number. Providing each of the first and fourth chain-link converters with a second, greater number of series-connected chain-link
AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
modules allows the combined first and second voltage source converters to withstand a worst case transient fault condition in terms of voltage stress on individual energy storage devices, i.e. an internal AC phase to return conduit, e.g., ground, fault.
Meanwhile, limiting the number of series-connected chain-link modules included in each of the second and third chain-link converters to a lower, first number provides a given degree of converter performance but reduces the total number of chain-link modules in each voltage source converter, and so leads to a significant reduction in the capital cost of the converter station. Additionally, having a reduced total number of chain-link modules provides the option of reducing the size of the overall structure and footprint of each chain-link converter, as well as lowering the switching losses associated with each chain-link converter which allows the use of a smaller cooling plant to service the chain-link converters, and thereby provides still further options for reducing the overall footprint, and hence cost, of the associated converter station. Having a reduced total number of chain-link modules also lessens the maintenance burden and allows operators to carry fewer spare chain-link modules for use in case of failure.
ABB additionally fails to hint at the possibility or any of the aforementioned benefits of the second and third chain-link converters having a different number of modules compared to the first and fourth chain-link converters. Hence there is no point in ABB that would have prompted the skilled person to consider adapting the converter station (900) of ABB to have a different number of chain-link modules in the second and third chain-link converters (300) compared to the first and fourth chain-link converters (300). Without such prompt or motivation, the skilled person would not have modified the converter station (900) in ABB in a way that would have resulted in the claimed invention.
AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
The Applicant thus asserts that independent claim 9, and the dependent claims thereon, are patentable over the cited reference. The same logic applies to independent claim 16.
35 U.S.C. § 103:
Claim 14 was rejected under 35 U.S.C. § 103 as allegedly being unpatentable over ABB, as cited above, in view of U.S. Patent Publication No. 2013/0182467 to Cross (Cross). The Applicant respectfully traverses the rejection for the reasons described above.
Allowed Claim
Applicant thanks the Examiner for indicating that claim 15 would be allowed if rewritten in independent form.
AMENDMENTS AND RESPONSE TO NON-FINAL OFFICE ACTION
CONCLUSION

NEXT OFFICE ACTION: DETAILED ACTION
This Office action is in response to the application/amendment filed on .
Notice of Pre-AIA  or AIA  Status
The present application, filed on or after March 16, 2013, is being examined under the first inventor to file provisions of the AIA .
In the event the determination of the status of the application as subject to AIA  35 U.S.C. 102 and 103 (or as subject to pre-AIA  35 U.S.C. 102 and 103) is incorrect, any correction of the statutory basis (i.e., changing from AIA  to pre-AIA ) for the rejection will not be considered a new ground of rejection if the prior art relied upon, and the rationale supporting the rejection, would be the same under either status.
This application currently names joint inventors. In considering patentability of the claims the examiner presumes that the subject matter of the various claims was commonly owned as of the effective filing date of the claimed invention(s) absent any evidence to the contrary.  Applicant is advised of the obligation under 37 CFR 1.56 to point out the inventor and effective filing dates of each claim that was not commonly owned as of the effective filing date of the later invention in order for the examiner to consider the applicability of 35 U.S.C. 102(b)(2)(C) for any potential 35 U.S.C. 102(a)(2) prior art against the later invention.
Response to Arguments
Applicant's arguments filed 19 November 2024 have been fully considered but they are not persuasive.
Regarding the objection to the drawings, Applicant cites to 37 CFR 1.81(a)-(b) and argues that, “a patent application is not required to show every detail of every possible embodiment of an invention in the drawings where a person having ordinary skill in the art would understand the subject matter sought to be patented in view of the drawings provided and corresponding portions of the specification” (Remarks, p. 7).
However, it is respectfully pointed out that the objection to the drawings did not suggest any requirement for Applicant to show all details or embodiments of the disclosed invention. Rather, the objection was presented under 37 CFR 1.83(a), which states that, “the drawing in a nonprovisional application must show every feature of the invention specified in the claims”, whereas by contrast, conventional or unessential features, “should be illustrated in the drawing in the form of a graphical drawing symbol or a labeled representation (e.g., a labeled rectangular box)”.
In this case, the feature at issue – namely, that the second and third chain-link converters include first number of series-connected chain-link modules, whereas the first and fourth chain-link converters include a second number of chain-link modules, the second number being greater than the first number – is both described in detail in the specification and falls within the language of the claims, and must therefore be shown in the drawings. Any structural detail that is of sufficient importance to be described should be shown in the drawing. (Ex parte Good, 1911 C.D. 43, 164 OG 739 (Comm’r Pat. 1911).)
Moreover, the feature is not merely a recitation of a known or conventional feature of converter stations in power transmission systems, but rather is one of the essential features that serves to define Applicant’s disclosed invention – see, e.g., Specification from p. 2, l. 20 through p. 3, l. 3. Indeed, in later arguments against the prior art rejections (addressed below), Applicant even relies on the limitations in claims 9 and 16 corresponding to this disclosed feature as the alleged point of novelty in view of the applied prior art. Thus, it is clear that the feature, at least as it is described in the specification, is essential to the understanding of the invention if it can potentially serve as the basis for eventual grant of patent rights.
Therefore, the objection to the drawings has been maintained in this Office action, it being respectfully submitted that making such requirement for correction is specifically imposed upon the examiner by paragraph (c) of 37 CFR 1.83, which states in part that, “where the drawings . . . do not comply with the requirements of paragraphs (a) and (b) of this section, the examiner shall require such additional illustration”.
Regarding the prior art rejection under 35 U.S.C. 102, Applicant argues that ABB (WO 2019/161907) does not show the same feature discussed above with respect to the drawing objection – i.e., that, “each of the second and third chain-link converters includes a first number of series-connected chain-link modules, and each of the first and fourth chain-link converters includes a second number of series-connected chain-link modules, the second number being greater than the first number”, as recited in claim 9 and similarly recited in claim 16.
Preliminarily, Examiner is in agreement as far as the disclosed embodiment of this aspect of the invention is concerned. That is, ABB and the additionally cited prior art indeed do not show the first and fourth chain-link converters as each having or consisting of a greater total number of chain-link modules than are contained in the each of the second and third chain-link converters.
However, Applicant has not addressed in the remarks the specific interpretation of this limitation of claims 9 and 16 that was made explicit in the non-final Office action. That is, under the heading of “Claim Interpretation”, the Examiner stated that, consistent with MPEP 2111.03, subsection I, the use of “including” in the claims was being interpreted in the same manner as typically applied to the term “comprising”. Thus, “including” was understood to only limit the claim scope to an open-ended construction of any claim limitation in which it appeared.
The explanation went on to specifically point out the limitation at issue in Applicant’s argument, which would be interpreted such that the second and third chain-link converters require at least the first number of chain-link modules, and similarly such that the first and fourth chain-link converters require at least the second number of chain link converters. This interpretation is considered to be a reasonably broad one in light of the MPEP, as cited above, specifically providing for the definition of the term “includes” or “including” that has been applied to the claims as presented.
At the risk of belaboring the point, but nonetheless for the sake of clarity as to the applied interpretation of claim scope, Examiner very respectfully offers another hypothetical, illustrative example: consider a prior art converter station (which could be modeled after that disclosed in ABB), which comprises first through fourth chain-link converters in the manner of the claims under examination. Each of the first through fourth chain-link converters may have exactly three chain-link modules.
In the above hypothetical scenario, because any group of exactly three modules inherently includes at least two modules, it would be logically true that the second and third chain-link converters each “include” two chain-link modules. Similarly, it would also be logically true that the first and fourth chain-link converters each “include” three chain-link modules since they each have exactly three modules as stated. In terms of the claimed terminology, the “first number” would be two and the “second number” would be three, and the hypothetical prior art converter station would anticipate the interpreted scope of the claimed limitations.
To overcome the rejection of independent claims 9 and 16 given the applied interpretation, it is suggested that Applicant re-draft the limitations at issue to use the term “consists” or “consisting”. For example, the limitation could be amended to recite:
each of the second and third chain-link converters consists of a first number of series-connected chain-link modules and each of the first and fourth chain-link converters consists of a second number of series-connected chain-link modules, the second number being greater than the first number.
The above limitation, considered in light of MPEP 2111.03, subsection II, would preclude the current interpretation from being reasonably applied, and, at least under the Examiner’s current presumption that the closest relevant prior art has been identified and made of record by a relevant party in this application’s file wrapper, would be considered allowable over such prior art.
Claim Rejections - 35 USC § 102
The following is a quotation of the appropriate paragraphs of 35 U.S.C. 102 that form the basis for the rejections under this section made in this Office action:
A person shall be entitled to a patent unless –
(a)(1) the claimed invention was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention.
(a)(2) the claimed invention was described in a patent issued under section 151, or in an application for patent published or deemed published under section 122(b), in which the patent or application, as the case may be, names another inventor and was effectively filed before the effective filing date of the claimed invention.
Claims 9-13 and 16 are rejected under 35 U.S.C. 102(a)(1) and 102(a)(2) as being anticipated by WO 2019/161907 A1 to ABB SCHWEIZ AG (hereinafter “ABB”).
In re claim 9, ABB discloses a converter station for a bipole power transmission scheme (Figs. 8-9; p. 9, l. 9-24), comprising:
a first voltage source converter (801) having a first terminal (see annotated version of Fig. 9 of ABB, below) for connection to a first transmission conduit (832), a second terminal (see annotated figure) for connection to a return conduit (connection between the VSCs 801 and 802; see p. 9, l. 8-15 and p. 14, l. 23-31), and at least one converter limb (Fig. 9: converter limb connected to AC terminal 872) extending between the first and second terminals (see annotated figure), the or each converter limb including first and second limb portions (reactors and sub-module chains on either side of AC terminal 872) separated by a corresponding first AC terminal (872) for connection to a respective phase of a first AC network (860a),
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the or each first limb portion including a first chain-link converter (see annotated figure) extending between the associated first AC terminal (872) and the first terminal (see annotated figure),
the or each second limb portion including a second chain-link converter (see annotated figure) extending between the associated first AC terminal (872) and the second terminal (see annotated figure), and
each chain-link converter including a plurality of series connected chain-link modules (see annotated figure) each having a plurality of switching elements connected in parallel with an energy storage device (see example sub-modules/modules as shown in Figs. 1-3) whereby each chain-link converter is controllable to provide a stepped variable voltage source (p. 1, l. 17 – p. 2, l. 12); and
a second voltage source converter (Figs. 8, 9: 802; see the annotated Fig. 9 provided above; in addition, the citations/explanations provided above for the first VSC 801 apply, mutatis mutandis, to the second VSC 802, therefore the citations will not be repeated) having a third terminal for connection to a second transmission conduit, a fourth terminal for connection to the return conduit, and at least one converter limb extending between the third and fourth terminals, the or each converter limb including third and fourth limb portions separated by a corresponding second AC terminal for connection to a respective phase of a second AC network, the or each third limb portion including a third chain-link converter extending between the associated second AC terminal and the third terminal, the or each fourth limb portion including a fourth chain-link converter extending between the associated second AC terminal and the fourth terminal, and each chain-link converter including a plurality of series connected chain-link modules each having a plurality of switching elements connected in parallel with an energy storage device whereby each chain-link converter is controllable to provide a stepped variable voltage source,
wherein the second terminal and the fourth terminal are electrically connected to one another (see the annotated Fig. 9, above: the second terminal and fourth terminal are electrically connected to one another at least by the illustrated switches 837, 839 being closed/conductive: see p. 24, ll. 11-14),
each of the second and third chain-link converters (see annotated figure, above) including a first number of series-connected chain-link modules (in the simplest case shown in Fig. 9, the first number may equal one; but see also p. 16, l. 11-20 and p. 25, l. 1-4: in other cases having more sub-modules in each converter, the first number may equal any other number that is less than the total number of sub-modules connected in the respective chain-link converter), and
each of the first and fourth chain-link converters (see annotated figure) including a second number of series-connected chain-link modules (in the simplest case, the second number is equal to two; or in other cases with more sub-modules than are shown in Fig. 9, the second number may be equal to the total number of sub-modules in a respective chain-link converter),
the second number being greater than the first number (in all cases as described above – i.e., 2>1, and the total number of sub-modules in either the first or fourth chain-link converter is greater than a number, less than said total, as found in either the second or third chain-link converter).
In re claim 16, the method of operation, as claimed, is largely directed to defining the structure of the converter station, the limitations of which are essentially identical to those of the apparatus of claim 9. Whereas the actual steps of the method itself constitute a rephrasing of the structural limitations found at the end of claim 9 regarding the number of chain-link modules in the first through fourth chain-link converters. Therefore, since ABB anticipates the converter station of claim 9 as explained above, ABB also inherently anticipates the method of operating the converter station as recited in claim 16, and the detailed citations and explanations will not be repeated.
In re claims 10-12, ABB discloses wherein each of the second and third chain-link converters include the same first number of series-connected chain-link modules (see annotated Fig. 9 of ABB, above – e.g., the second and third converters each include one module); wherein each of the first and fourth chain-link converters (see annotated figure) include the same second number of series-connected chain-link modules (e.g., they each include two modules as shown); and wherein each chain-link module has the same topology (see, e.g., p. 3, l. 27-32: in embodiments having larger numbers of sub-modules in each limb portion, it is sufficient to consider only the HB modules or only the FB modules as corresponding to the chain-link modules of the claimed invention).
In re claim 13, ABB discloses wherein each chain-link module (in the case of only considering HB modules/sub-modules as explained above from claim 12; see Fig. 2) includes a first pair of switching elements (IGBTs in Fig. 2) connected in parallel with the energy storage device (204) in a half-bridge arrangement to define a 2-quadrant unipolar module (Fig. 2).
Claim Rejections - 35 USC § 103
The following is a quotation of 35 U.S.C. 103 which forms the basis for all obviousness rejections set forth in this Office action:
A patent for a claimed invention may not be obtained, notwithstanding that the claimed invention is not identically disclosed as set forth in section 102, if the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art to which the claimed invention pertains. Patentability shall not be negated by the manner in which the invention was made.
Claim 14 is rejected under 35 U.S.C. 103 as being unpatentable over ABB, as cited above, in view of Cross et al. (US 2013/0182467; hereinafter “Cross”).
In re claim 14, ABB discloses the invention according to claim 9 as explained above, and further discloses wherein at least one voltage source converter includes a corresponding voltage source converter controller (p. 11, l. 26-33) programmed to control the stepped variable voltage source provided by the said corresponding voltage source converter (id.).
ABB does not disclose that the controller is programmed to balance the total energy stored by the energy storage devices in one limb portion of the said voltage source converter with the total energy stored by the energy storage devices in the other corresponding limb portion of the voltage source converter.
Whereas Cross discloses a chain-link converter (Figs. 1B, 2) and associated controller and method in which the voltage and consequently, the energy, stored in each of the individual chain-link module capacitors (i.e., energy storage devices) are balanced ([0086], [0093]-[0094]). As a result, the total energy stored by the modules in each of the limb portions will likewise be balanced. The balancing control is performed in order to reduce or eliminate DC voltage variations or oscillations for improved operation in an HVDC system ([0011]).
Therefore it would have been obvious to a person of ordinary skill in the art before the effective filing date of the claimed invention to have modified the converter station of ABB such that the controller is programmed to balance the total energy stored by the energy storage devices in one limb portion of the said voltage source converter with the total energy stored by the energy storage devices in the other corresponding limb portion of the voltage source converter as taught by Cross, for the purpose of improving performance of the HVDC transmission system by reducing or eliminating DC voltage variations or oscillations.
Allowable Subject Matter
Claim 15 is objected to as being dependent upon a rejected base claim, but would be allowable if rewritten in independent form including all of the limitations of the base claim and any intervening claims.
The following is a statement of reasons for the indication of allowable subject matter:
It is first noted that while no claim besides claim 15 can be objected to as containing allowable subject matter in its present form, the Examiner nonetheless has indicated in the Response to Arguments, above, that a re-drafting of the final limitation in claims 9 and 16 would render such claims (as well as those depending therefrom) allowable. Such allowability is necessarily predicated on the claims being amended specifically as stated above, but it is likely that other amendments could be made to equally capture the novel and unobvious aspect of the disclosed invention that has been identified. The reasons for this indication of allowable subject matter are believed to be clearly understood from the prosecution history as a whole, including the discussions above in this Office action, and therefore they are not repeated here.
Further, regarding claim 15 specifically, the reasons for indicating allowable subject matter, as provided in the previous Office action dated 19 September 2024, remain essentially unchanged in substance and are therefore also not repeated here.
Conclusion
THIS ACTION IS MADE FINAL.  See MPEP § 706.07(a).  Applicant is reminded of the extension of time policy as set forth in 37 CFR 1.136(a).
A shortened statutory period for reply to this final action is set to expire THREE MONTHS from the mailing date of this action.  In the event a first reply is filed within TWO MONTHS of the mailing date of this final action and the advisory action is not mailed until after the end of the THREE-MONTH shortened statutory period, then the shortened statutory period will expire on the date the advisory action is mailed, and any extension fee pursuant to 37 CFR 1.136(a) will be calculated from the mailing date of the advisory action.  In no event, however, will the statutory period for reply expire later than SIX MONTHS from the date of this final action.

CITED REFERENCE SUMMARIES: Ref US20130182467A1: [content unavailable]
Ref WO2014111595A1: Claims:
A multilevel converter (10) configured to convert between alternating current (AC) and direct current (DC) and comprising
at least one phase arm with a number of cells between a DC pole (PI; P2) and a first AC terminal (ACA1), said cells comprising at least one hybrid full bridge cell (HFBA; HFBB, HFBC; HFBD) for fault current handling operation,
said hybrid full-bridge cell comprising
a first cell connection terminal for coupling to the DC pole,
a second cell connection terminal for coupling to the AC terminal,
an energy storage element (C) having a positive and a negative end
a first group of series connected semiconducting units, which group is connected in parallel with the energy storage element (C) and where the semiconducting units (SU1, SU2) of the first group comprises first and second switching elements (Tl, T2) with first and second anti-parallel unidirectional conducting elements (Dl, D2), where a junction between the first and second semiconducting unit forms one cell connection terminal (TEFBA1; TEFBB1; TEFBC2; TEFBD2),
a second group of semiconducting units, which group is connected in parallel with the energy storage element (C) as well as with the first group and where all the semiconducting units of the second group are connected in series and the second group comprises a third semiconducting unit (SU3) having a third switching element (T3) with anti-parallel unidirectional 

conducting element (D3) and a fourth semiconducting unit (SU4) consisting of at least one unidirectional conducting element (D) , where a junction between the first and second semiconducting unit forms a further cell connection terminal (TEFBA2; TEFBB2; TEFBC1;
The multilevel converter according to claim 1, wherein the third switching element (T3) of the third semiconducting unit (SU3) in the second group is always configured to be on in normal operation of the
The multilevel converter according to claim 1 or 2, wherein all switching elements of the hybrid full- bridge cell are configured to be turned off if a fault current due to a DC pole fault runs through the phase arm.
The multilevel converter according to any previous claim, wherein the direction of conduction of the unidirectional conducting elements of the hybrid full- bridge cell is toward the positive end of the energy storage element.
The multilevel converter according to any previous claim, wherein the fourth semiconducting unit couples the energy storage element between the first and the second cell connection terminal with a polarity that counteracts negative currents in the phase arm.
The multilevel converter according to any previous claim, further comprising a control unit (12) 

configured to control, when there is a pole fault on a phase leg in which said phase arm is connected, a phase arm current (lap, Ian) to zero when there is a negative phase arm voltage (Vap, Van) during injection of reactive power through the first AC terminal.
The multilevel converter according to claim 6, wherein the control involves controlling a circulating current (Iacir) of the phase leg.
The multilevel converter according to claim 7, wherein the control unit comprises a circulating current control element (18) configured to provide a circulating current driving voltage (Vacir*).
The multilevel converter according to claim 8, wherein the circulating current control element (18) comprises a a subtracting block (34) configured to subtract the actual circulating current from the desired circulating current and supply the results to a proportional and/or integrating control block (34) configured to perform proportional and/or integrating control on said results for obtaining a first control voltage value used in obtaining the circulating current driving voltage.
The multilevel converter according to claim 9, further comprising an adding block (38) configured to add a control term to the first control voltage value for obtaining the circulating current driving voltage, where the control term is dependent on the time
derivative of the circulating current.
The multilevel converter according to any previous claim, wherein said phase arm with hybrid full-bridge cell (HFBA; HFBC) is provided in a first phase arm between a first pole (PI) and a first AC terminal (ACA1) .
The multilevel converter according to any previous claim 11, further comprising a second phase arm between the first AC terminal and ground, wherein the energy storage elements of all the converter cells of the second phase arm are configured to be bypassed in case of a phase fault on the AC side of the multilevel converter .
The multilevel converter according to claim 12, wherein all cells of the second phase arm are half- bridge cells, the energy storage elements of which are automatically bypassed as the semiconducting switches are blocking during such AC side faults.
The multilevel converter according to claim 12 or
wherein at least some of the cells of the second phase arm are hybrid full-bridge cells (HFBD) , each comprising a bypass switch (TH) controllable to bypass the corresponding energy storage element.
The multilevel converter according to claim 14, wherein the bypass switch is provided as a part of the third semiconducting unit (SU3) .
The multilevel converter according to claim 14, wherein the bypass switch is connected between cell connection terminals (TEFBD1, TEFBD2) .
The multilevel converter according to any of claims 12 - 16, the phase leg further comprising a third phase arm between a second AC terminal (ACA2) and ground and a fourth phase arm between the second AC terminal
(ACA2) and a second pole, wherein the fourth phase arm comprises at least one hybrid full-bridge cell and the energy storage elements of all the converter cells of the third phase arm are configured to be bypassed in case of a phase fault on the AC side of the multilevel converter .
A method of controlling a phase arm of a phase leg in a voltage source converter converting between alternating current (AC) and direct current (DC) and comprising at least one phase arm with a number of cells according to any of claims 1 - 5, the method comprising
controlling, when there is a pole fault on a pole of a phase leg in which said phase arm is connected, a phase arm current (lap, Ian) to zero when there is a negative phase arm voltage (Vap, Van) during injection of reactive power through the first AC terminal (ACA1) .
The method according to claim 18, wherein the controlling comprises controlling a circulating current (Iacir) of the phase leg.
The method according to claim 19, wherein the controlling comprises providing a circulating current driving voltage (Vacir*) based on a control loop for the circulating current.
The method according to claim 20, wherein the controlling comprises applying a proportional and/or integrating control on the difference between the desired and actual circulating current (Iacir*. Iacir) for obtaining a first control voltage value used in obtaining the circulating current driving voltage.
The method according to claim 21, wherein the control comprises adding a control term to the first control voltage value for obtaining the circulating current driving voltage, where the control term is dependent on the time derivative of the circulating current .
A method for reducing the voltage rating required for a phase arm in a voltage source converter
configured to convert between alternating current (AC) and direct current (DC) and comprising a first phase arm between a first pole (PI) and a first AC terminal (ACA1) with a number of cells according to any of claims 1 - 5 and a second phase arm between the first AC terminal and ground, where at least some of the cells of the second phase arm are hybrid full-bridge cells
where the method comprises controlling the energy storage elements of all the hybrid full-bridge cells of the second phase arm to be bypassed in case of a phase fault on the AC side of the multilevel converter.
The method according to claim 23, wherein all the hybrid full-bridge cells of the second phase arm comprise a bypass switch (TH) and the controlling comprises activating the bypass switches to bypass 

corresponding energy storage elements when the phase fault occurs on the AC side of the multilevel converter .
The method according to claim 23 or 24, where the fault occurs on another phase than the phase to which the first AC terminal is connected.
Ref WO2015110185A1: Claims:
A multilevel converter (10) configured to convert between alternating current (AC) and direct current (DC) and comprising
a phase leg (PL1) having a first and a second phase arm, said first phase arm being connected between a first pole (PI) and a first AC terminal (ACA1) and the second phase arm being connected between the first AC terminal (ACA1) and ground,
said phase leg comprising cells of a first type (HBA; HBB) having a unipolar voltage contribution and cells of a second type (FBA; FBB) having a bipolar voltage contribution, where each cell comprises at least one energy storage element (C) for providing said voltage contribution and cell switches (SI, S2, S3, S4; S5, S6) for controlling the voltage contribution,
wherein the first phase arm comprises cells of the second type and the energy storage elements of all the converter cells of the second phase arm are configured to be bypassed in case of a phase fault on the AC side of the multilevel converter.
The multilevel converter according to claim 1, wherein all cells of the second phase arm are cells of the first type, the energy storage elements of which are automatically bypassed as the cell switches are blocked during such AC side faults.
The multilevel converter according to claim 2, wherein all cells of the first phase arm are cells of the second type.
The multilevel converter according to claim 1, wherein at least some of the cells of the second phase arm are cells of the second type, each comprising a bypass switch (TH) controllable to bypass the
corresponding energy storage element.
The multilevel converter according to claim 4, wherein the bypass switch is provided as a part of a cell switch used in control of the voltage contribution by the cell.
The multilevel converter according to claim 4, wherein the bypass switch is connected between cell connection terminals (TEFBB1, TEFBB2) used for
connecting the cell to the phase arm.
The multilevel converter according to any previous claim, further comprising a control unit (12)
configured to control, when there is a pole fault on a pole connected to an AC terminal via a phase arm, the cells of another phase arm connected between the AC terminal and ground to synthesize an AC voltage
waveform for injecting reactive power into the AC terminal .
The multilevel converter according to claim 7, wherein the waveform comprises a DC component that has a value being half the pole voltage.
The multilevel converter according to any previous claim, the phase leg further comprising a third phase arm between a second AC terminal (ACA2) and ground and a fourth phase arm between the second AC terminal and a 

second pole (P2), wherein the fourth phase arm
comprises at least one cell of the second type and the energy storage elements of all the converter cells of the third phase arm are configured to be bypassed in case of a phase fault on the AC side of the multilevel converter .
A method of controlling fault handling in a phase leg (PL1) of a multilevel converter converting between alternating current (AC) and direct current (DC) , the phase leg (PL1) having a first and a second phase arm, said first phase arm being connected between a first pole (PI) and a first AC terminal (ACA1) and the second phase arm being connected between the first AC terminal (ACA1) and ground, said phase leg comprising cells of a first type having a unipolar voltage contribution and cells of a second type having a bipolar voltage
contribution, where each cell comprises at least one energy storage element for providing said voltage contribution and cell switches (SI, S2, S3, S4; S5, S6) for controlling the voltage contribution, the method comprising
upon the detection of a phase fault on the AC side of the multilevel converter,
blocking cell switches of the cells in the phase leg, and
controlling the energy storage elements of all the converter cells in the second phase arm to be bypassed.
The method according to claim 10, wherein at least some of the cells of the second phase arm are cells of the second type, each comprising a bypass switch (TH) 

and the controlling comprises activating the bypass switches to bypass corresponding energy storage
elements when the phase fault occurs on the AC side of the multilevel converter.
The method according to claim 11, wherein at least one bypass switch is provided as a part of a cell switch used in control of the voltage contribution by a corresponding cell.
The method according to claim 11 or 12, wherein at least one bypass switch is connected between cell connection terminals (TEFBB1, TEFBB2) used for
connecting a corresponding cell to the phase arm.
The method according to any of claims 10 - 13, the phase leg further comprising a third phase arm between a second AC terminal (ACA2) and ground and a fourth phase arm between the second AC terminal (ACA2) and a second pole (P2), the method further comprising
controlling the energy storage elements of all the converter cells in the third phase arm to be bypassed in case of a phase fault on the AC side of the
multilevel converter.
The method according to any of claims 10 - 14, wherein the fault occurs on another phase than the phase to which the first AC terminal is connected.
The method according to any of claims 10 - 15, further comprising detecting a DC fault on a pole (PI) connected to an AC terminal via a phase arm, blocking the switches of the cells of the phase leg until a DC 

fault current is cleared, deblocking, after clearing of a DC fault current, the cells of another phase arm connected between the AC terminal and ground and controlling the deblocked cells to synthesize an AC voltage waveform for injecting reactive power into the AC terminal .
Ref CN106160545A: Claims:
A bridge-arm hybrid bipolar modular multilevel converter, characterized in that it includes a positive modular multilevel converter and a negative modular multilevel converter both composed of three phases , and two transformers; among them, the positive DC terminal of the positive pole modular multilevel converter is used as the positive pole DC bus of the bridge arm hybrid bipolar modular multilevel converter, and the positive pole modular multilevel converter The negative DC terminal of the inverter is connected to the positive terminal of the negative pole modular multilevel converter, which serves as the ground pole DC bus of the bridge arm hybrid bipolar modular multilevel converter, and the negative pole modular multilevel converter The negative DC terminal of the bridge arm is used as the negative DC bus of the bridge arm hybrid bipolar modular multilevel converter; the three-phase AC side outgoing terminal of the positive modular multilevel converter is connected to the first transformer (TR1) The three-phase outlet terminals of the secondary side are connected, and the three-phase outlet terminals of the primary side of the first transformer are connected with the external AC grid in three phases; the three-phase AC side outlet terminals of the negative modular multilevel converter are connected with the second transformer (TR2) The secondary three-phase outlet of the second transformer is connected to the three-phase outlet of the primary side of the second transformer with the external AC power grid in three phases; The three-phase structure constituting the positive modular multilevel converter is the same, and each phase is composed of two different bridge arms of the clamp sub-module type bridge arm and the half-bridge sub-module type bridge arm; in each phase, the clamp The positive terminal of the sub-modular bridge arm is used as the positive terminal of the DC side of the phase, the negative terminal of the half-bridge sub-modular bridge arm is used as the negative terminal of the phase DC side, and the negative terminal of the clamp sub-modular bridge arm is connected with the half-bridge sub-modular bridge. The positive terminals of the three-phase DC side are connected to each other as the outlet terminal of the AC side of each phase; the positive terminals of the three-phase DC side are connected to serve as the positive DC terminal of the positive modular multilevel converter; the negative terminals of the three-phase DC side are connected to serve as the positive terminal of the modular multilevel converter. The negative DC terminal of the level converter; The three-phase structure constituting the negative pole modular multilevel converter is the same, and each phase is composed of two different bridge arms of the clamp sub-module type bridge arm and the half-bridge sub-module type bridge arm; in each phase, the clamp The negative terminal of the sub-modular bridge arm is used as the negative terminal of the DC side of the phase, the positive terminal of the half-bridge sub-modular bridge arm is used as the positive terminal of the phase DC side, and the positive terminal of the clamp sub-modular bridge arm is connected with the half-bridge sub-modular bridge. The negative terminals of the three-phase DC side are connected to each other as the outlet terminal of the AC side of each phase; the positive terminals of the three-phase DC side are connected to serve as the positive DC terminal of the negative modular multilevel converter; the negative terminals of the three-phase DC side are connected to serve as the negative terminal of the modular multilevel converter. The negative DC terminal of the level converter.
A bridge-arm hybrid bipolar modular multilevel converter, characterized in that it includes a positive modular multilevel converter and a negative modular multilevel converter both composed of three phases , and two transformers; among them, the positive DC terminal of the positive pole modular multilevel converter is used as the positive pole DC bus of the bridge arm hybrid bipolar modular multilevel converter, and the positive pole modular multilevel converter The negative DC terminal of the inverter is connected to the positive terminal of the negative pole modular multilevel converter, which serves as the ground pole DC bus of the bridge arm hybrid bipolar modular multilevel converter, and the negative pole modular multilevel converter The negative DC terminal of the bridge arm is used as the negative DC bus of the bridge arm hybrid bipolar modular multilevel converter; the three-phase AC side outgoing terminal of the positive modular multilevel converter is connected to the first transformer (TR1) The three-phase outlet terminals of the secondary side are connected, and the three-phase outlet terminals of the primary side of the first transformer are connected with the external AC grid in three phases; the three-phase AC side outlet terminals of the negative modular multilevel converter are connected with the second transformer (TR2) The secondary three-phase outlet of the second transformer is connected to the three-phase outlet of the primary side of the second transformer with the external AC power grid in three phases;
The three-phase structure constituting the positive modular multilevel converter is the same, and each phase is composed of two different bridge arms of the clamp sub-module type bridge arm and the half-bridge sub-module type bridge arm; in each phase, the clamp The positive terminal of the sub-modular bridge arm is used as the positive terminal of the DC side of the phase, the negative terminal of the half-bridge sub-modular bridge arm is used as the negative 
[Truncated to input limit]