Office Action 2: Final Rejection (2024-11-27)
Rejection types: 102 - Lack of Novelty, 103 - Obviousness, 112 - Written Description/Enablement

CLAIMS:
In the Claims:

AMENDMENTS

1.-8. (Cancelled)27

9\. (Currently amended) A converter station, for a bipole power transmission scheme, comprising:
a first voltage source converter having a first terminal for connection to a first transmission conduit, a second terminal for connection to a return conduit, and at least one converter limb extending between the first and second terminals, the or each converter limb including first and second limb portions separated by a corresponding first AC terminal for connection to a respective phase of a first AC network, the or each first limb portion including a first chain-link converter extending between the associated first AC terminal and the first terminal, the or each second limb portion including a second chain-link converter extending between the associated first AC terminal and the second 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; and
a second voltage source converter 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,
wherein 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.

10\. (Previously Presented) A converter station according to claim 9, wherein each of the second and third chain-link converters include the same first number of series-connected chain-link modules.

11\. (Previously Presented) A converter station according to claim 9, wherein each of the first and fourth chain-link converters include the same second number of series-connected chain-link modules.

12\. (Previously Presented) A converter station according to claim 9, wherein each chain-link module has the same topology.
13\. (Previously Presented) A converter station according to claim 12, wherein each chain-link module 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.

14\. (Currently amended) A converter station according to claim 9, wherein at least one of the first and second voltage source converters includes a corresponding voltage source converter controller programmed to control the stepped variable voltage source provided by the said corresponding voltage source converter, and when doing so 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.

15\. (Previously Presented) A converter station according to claim 14, wherein the at least one voltage source converter 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.

16\. (Currently amended) A method of operating a converter station comprising:
a first voltage source converter having a first terminal connected to a first transmission conduit, a second terminal connected to a return conduit, and at least one converter limb extending between the first and second terminals, the or each converter limb
including first and second limb portions separated by a corresponding first AC terminal connected to a respective phase of a first AC network, the or each first limb portion including a first chain-link converter extending between the associated first AC terminal and the first terminal, the or each second limb portion including a second chain-link converter extending between the associated first AC terminal and the second 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; anda second voltage source converter having a third terminal connected 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 connected to a respective phase of a second AC network, the third limb portion including a third chain-link converter extending between the associated second AC terminal and the third terminal, the 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,
the method comprising the steps of:
providing each of the second and third chain-link converters with a first number of series- connected chain-link modules; and

providing each of the first and fourth chain-link converters with a second number of series-connected chain-link modules, the second number being greater than the first number.

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),
PNG
media_image1.png
647
574
media_image1.png
Greyscale
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.

APPLICANT REBUTTAL: AMENDMENT AND RESPONSE TO FINAL OFFICE ACTION

AMENDMENTS TO THE DRAWINGS
Replacement sheet is submitted herewith for FIG. 1. No new matter has been added.
Attachment: Replacement Sheet for FIG 1

NEXT OFFICE ACTION: Drawings
The drawing amendments, as received on 31 January 2025, are acceptable.
Allowable Subject Matter
Claims 9-16 are allowed.
Independent claims 9 and 16 have been amended by Applicant substantially in accordance with the language previously suggested by the examiner. As such, the claims stand allowable for the same reasons as have already been explained on record—see the Final Rejection dated 27 November 2024.
Conclusion

CITED REFERENCE SUMMARIES: Ref WO2019161907: Claims:
1. A method of starting operation of a converter (400, 500) of a high voltage direct current, HVDC, converter station, wherein said converter is a modular multilevel converter, MMC, including, at a direct current, DC, side (420), two DC terminals (422, 424) for connection to a DC transmission system (430) and, at an alternating current, AC, side (410), AC connectors (472, 474, 476) connectable to electrical phase lines (442, 444, 446) of an AC power source (440), wherein said converter includes valve arms (550) each connected between a DC terminal and an AC connector for connection to one electrical phase line, wherein each valve arm includes at least one full-bridge, FB, submodule (305) and at least one half-bridge, HB, submodule (310) connected in series, said method comprising:
establishing (S610, S710) a direct electrical connection between the
DC terminals of the converter;
electrically connecting (S620, S720) the converter to the AC power source via said AC connectors;
obtaining (S630, S730), from the AC power source and for a certain period of time, an AC voltage between two electrical phase lines for charging capacitors of the FB submodules connected to said two electrical phase lines; and
controlling (S640, S750), after said period of time, switching devices of the FB submodules for charging capacitors of the FIB submodules to at least a minimum voltage required to start switching switching devices of the FIB submodules.
2. The method of claim 1 , further comprising activating (S650, S760) control of switching devices of the FIB submodules once they are charged to at least said minimum voltage and maintaining a DC voltage at approximately the same level as the level reached before said activating control of the switching devices of the FIB submodules.
3. The method of claim 1 or 2, wherein the capacitors are charged by drawing electrical power from the AC power source via the electrical phase lines connected thereto.
4. The method of any one of the preceding claims, wherein the converter is configured to support the AC side with reactive power while charging the capacitors of the HB submodules to at least said minimum voltage.
5. The method of any one of the preceding claims, further comprising: electrically disconnecting (S660) the DC terminals of the converter from each other after that the capacitors of the HB submodules are charged to at least said minimum voltage; and
electrically connecting (S660) the DC terminals to the DC transmission system.
6. The method of any one of claims 1 -4, further comprising:
electrically disconnecting (S740) the DC terminals of the converter from each other before controlling the switching devices of the FB
submodules for charging the capacitors of the HB submodules to at least said minimum voltage, and
electrically connecting (S740) the DC terminals to the DC transmission system.
7. The method of any one of claims 5-6, further comprising starting
(S670, S770) a DC voltage ramp to a selected value for transferring/receiving electrical power once the DC terminals are connected to the DC transmission system and the capacitors of the FB submodules and the HB submodules are charged to their rated values.
8. A method of starting operation of a first converter (801 ) of an HVDC converter station (800, 900) including a second converter (802) connected in 

 series with said first converter, wherein said first converter is a modular multilevel converter connectable, at its DC side (821 ), to a DC transmission line (832) of a DC transmission system (830) via a first DC terminal (822) and, via a second DC terminal (828), to either one of another DC transmission line (834) of said transmission system or a DC terminal (826) of the second converter using a set of connectors (836, 837), wherein each valve arm of the first converter includes at least one FB submodule and at least one HB submodule, wherein said converter station includes a bypass switch (825) to bypass the first converter, wherein the first converter further includes, at its AC side (811 ), AC connectors (872, 874, 876) connectable to electrical phase lines (842, 844, 846) of an AC power source (840), wherein the second converter is initially in operation to transfer or receive electrical power and directly connected, at its DC side, to said DC transmission system via its two DC terminals, wherein the first converter is bypassed and electrically disconnected at its DC side from said DC transmission system and from the second converter using said set of connectors, said method including:
establishing (S1001 ) a direct electrical connection between the DC terminals of the first converter;
electrically connecting (S1002) the first converter to the AC power source;
obtaining (S1003), from the AC power source and for a certain period of time, an AC voltage between two electrical phase lines for charging capacitors of the FB submodules connected between said two electrical phase lines; and
controlling (S1004), after said period of time, switching devices of the FB submodules for charging capacitors of the FIB submodules to at least a minimum voltage required to start switching switching devices of the FIB submodules.
9. The method of claim 8, wherein said method includes steps as defined in any one of claims 2-4 for charging of the capacitors of the submodules of the first converter.
10. The method of claim 8 or 9, wherein said method includes electrically disconnecting (S1005) the DC terminals of the first converter from each other after that the capacitors of the HB submodules are charged to at least said minimum voltage or before controlling the switching devices of the FB submodules for charging the capacitors of the HB submodules to said at least minimum voltage.
11. The method of claim 10, further comprising electrically connecting (S1006) the first DC terminal to the DC transmission line of the DC
transmission system and electrically connecting the second DC terminal to a DC terminal of the second converter using said set of connectors.
12. The method of claim 11 , further comprising, once the first and second DC terminals of the first converter are connected to the DC transmission system and a DC terminal of the second converter, respectively, controlling (S1007) switching devices of the HB and FB submodules of the first converter such that a DC current flowing from the DC transmission system through the bypass switch is directed to the first converter.
13. The method of claim 12, further comprising opening (S1008) the bypass switch when the DC current becomes approximately zero across said bypass switch and increasing (S1009) a DC voltage across the first converter to a first selected value to transfer/receive electrical power to/from the DC transmission system.
14. The method of any one of claims 8-13, wherein the converter station further includes another bypass switch (890) to establish a direct electrical connection between the first and second DC terminals (822, 828) of the first converter.
15. A control unit adapted to control the charging of a converter in accordance with a method as defined in any one of the preceding claims.
16. A converter station adapted to transfer/receive electrical power, said converter station including a controller configured to operate at least one converter in accordance with a method as defined in any one of claims 1 -14.
Ref US20130182467: Claims:
1. A voltage source converter for use in high voltage direct current power transmission and reactive power compensation, the voltage source converter comprising three phase elements defining a star connection in which a first end of each phase element is connected to a common junction, each phase element being operably associated in use with a respective phase of a three-phase AC network and including at least one impedance element; at least two converter limbs, each converter limb including first and second DC terminals for connection in use to a DC network and an AC terminal connected in series with a second end of a phase element of the star connection, each converter limb defining first and second limb portions, each limb portion including a chain-link converter connected in series between a respective one of the first and second DC terminals and the respective AC terminal, each chain-link converter including a plurality of chain-link modules connected in series; and a third DC terminal connected between the first and second DC terminals, the third DC terminal being connected to the common junction of the star connection to define an auxiliary connection, wherein in use a current is injected into the auxiliary connection to achieve balance between the voltage levels of the individual chain-link modules of each chain-link converter of each limb portion.
2. A voltage source converter according to claim 1 further including at least one DC link capacitor connected in series between the third DC terminal and each of the first and second DC terminals.
3. A voltage source converter according to claim 1 wherein each phase element includes a primary impedance element connected in series with one or more secondary impedance elements, the primary impedance element being provided in the form of a transformer winding.
4. A voltage source converter according to claim 1 wherein each phase element includes a primary impedance element provided in the form of a transformer winding and the auxiliary connection includes at least one secondary impedance element.
5. A voltage source converter according to claim 1 wherein the limb portions of each converter limb are operable in use to modulate a phase voltage of the respective phase of the three-phase AC network to provide a voltage across each secondary impedance element.
6. A voltage source converter according to claim 1 wherein the auxiliary connection includes a secondary impedance element connected in series with an additional chain-link converter between the common junction and the third DC terminal, said additional chain-link converter including a plurality of chain-link modules connected in series.
7. A voltage source converter according to claim 1 wherein the auxiliary connection includes a secondary impedance element provided in the form of an additional chain-link converter between the common junction and the third DC terminal, said additional chain-link converter including a plurality of chain-link modules connected in series.
8. A voltage source converter according to claim 6 wherein the additional chain-link converter of the auxiliary connection is operable in use to provide a voltage across each secondary impedance element.
9. A voltage source converter according to claim 1 wherein the voltage source converter includes three converter limbs, the AC terminal of each converter limb being connected in use to a second end of a respective phase element of the star connection.
10. A voltage source converter according to claim 1 wherein the voltage source converter further includes a chain-link converter connected between a second end of a phase element of the star connection and the third DC terminal, the chain-link converter including a plurality of chain-link modules connected in series.
11. A voltage source converter according to claim 1 wherein each limb portion further includes at least one switching element connected in series with the chain-link converter, each switching element being operable to switch the limb portion into and out of circuit.
12. A voltage source converter according to claim 1 wherein each chain-link module includes at least a pair of switching elements connected in parallel with an energy storage device, the semiconductor switches being operable in use such that each chain of modules connected in series provides a continuously variable voltage source.
13. A voltage source converter according to claim 1 wherein the switching elements of each chain-link module are connected with the respective energy storage device in a half-bridge arrangement to define a 2-quadrant unipolar module that can develop zero or positive voltage and can conduct current in both directions.
14. A voltage source converter according to claim 12 wherein the switching elements of each chain-link module are connected with the respective energy storage device in a full-bridge arrangement to define a 4-quadrant bipolar module that can develop positive, zero or negative voltage and can conduct current in both directions.
15. A voltage source converter according to claim 12 wherein the energy storage device in each chain-link module is provided in the form of a capacitor, fuel cell, battery or an auxiliary AC generator with an associated rectifier.
16. A voltage source converter according to claim 11 wherein each switching element includes a semiconductor device.
17. A voltage source converter according to claim 16 wherein the semiconductor device is an insulated gate bipolar transistor, field-effect transistor, gate turn-off thyristor or integrated gate-commutated transistor.
18. A voltage source converter according to claim 1 wherein each limb portion is operable to modify the voltage waveform at the AC terminal to present a near-approximation of a sinusoidal voltage waveform to the respective phase element of the star connection.
19. A voltage source converter according to claim 1 wherein the current injected in use into the auxiliary connection is a zero-phase sequence triple harmonic current.
20. A voltage source converter according to claim 1 wherein the chain-link converter in each limb portion is operable to generate a voltage to oppose the flow of current created by a fault in the AC or DC network.
21. A voltage source converter according to claim 1 wherein each phase element of the star connection is mutually coupled in use with a respective primary winding in which a first end of each primary winding is connected to a second end of a different primary winding such that the interconnection of the primary windings define a closed loop, and each junction between two primary windings is connected to a respective phase of a three-phase AC network.
22. A voltage source converter according to claim 1 wherein each phase element of the star connection is mutually coupled in use with a respective tertiary winding in which a first end of each tertiary winding is connected to a second end of a different tertiary winding such that the interconnection of the tertiary windings define a closed loop, and each junction between two tertiary windings is connected to an auxiliary network.