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 .
DETAILED ACTION
This Office Action is in response to Application No. 18/576136 filed on January 3, 2024. Claims 1-10 are presented for examination and are currently pending.
Claim Rejections - 35 USC § 101
35 U.S.C. 101 reads as follows:
Whoever invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent therefor, subject to the conditions and requirements of this title.
Claim 10 is rejected under 35 U.S.C. 101 because the claimed invention is directed to non-statutory subject matter. The claim(s) does/do not fall within at least one of the four categories of patent eligible subject matter because the claim is directed to a computer readable medium. Broadly and reasonably speaking the claim medium can be interpreted as transitory (i.e., signal per se); hence, the claim is directed to a signal and non-statutory subject matter.
Claim Rejections - 35 USC § 102
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(s) 1, 4, 5, 7 and 9 is/are rejected under 35 U.S.C. 103 as being unpatentable over Gadiraju (US 10,742,149) in view of Sojud ("Improving the Reactive Power Capability of the DFIG-Based Wind Turbine During Operation Around the Synchronous Speed," in IEEE Transactions on Energy Conversion, vol. 28, no. 3, pp. 736-745, Sept. 2013).
Regarding claim 1, Gadiraju a method for computer-implemented controlling a doubly-fed electric machine, where stator windings of a stator are directly connected to an electrical grid and where rotor windings of a rotor are connected to the electrical grid via a power conversion system [“The above system is generally referred to as a doubly-fed induction generator (DFIG) system, whose operating principles include that the rotor windings are connected to the grid via slip rings and the power converter controls rotor current and voltage.” (col. 1, lines 35-40)], comprising an AC-to-DC converter and a DC-to-AC converter and being adapted to control a rotor current [“The power converter 162 includes a rotor side converter (RSC) 166 and a line side converter (LSC) 168. The DFIG 120 is coupled via the rotor bus 156 to the rotor side converter 166. Additionally, the RSC 166 is coupled to the LSC 168 via a DC link 136 across which is a DC link capacitor 138. The LSC 168 is, in turn, coupled to a line side bus 188.” (col. 6, lines 60-65)], the method comprising:
a) obtaining a rotational speed of the doubly-fed electric machine [“feedback in the form of a sensed speed of the DFIG 120 may be used to control the conversion of the output power from the rotor bus 156 to maintain a proper and balanced multi-phase (e.g. three-phase) power supply.” (col. 8, lines 30-40)];
b) determining, whether the rotational speed is within a predetermined operational speed range around a synchronous speed; wherein, if it is determined that the rotational speed is within the predetermined operational speed range [“as the generator rotor speed changes and approaches synchronous speed, generating a control command to decrease a switching frequency of the switching elements from a first switching frequency to a second switching frequency, wherein the reactive power output of the power converter is increased at the second switching frequency” (col. 12, lines 10-20)], the following steps are performed:
c) controlling the AC-to-DC converter of the power conversion system to force injection of a stator reactive power to create a harmonic at a frequency different than a rated frequency of the doubly-fed electric machine [“Control of rotor voltage and current enables the generator to remain synchronized with the grid frequency while the wind turbine speed varies (e.g., rotor frequency can differ from the grid frequency). Also, the primary source of reactive power from the DFIG system is from the RSC via the generator (generator stator-side reactive power) and the LSC (generator line-side reactive power). Use of the power converter, in particular the RSC, to control the rotor current/voltage makes it is possible to adjust the reactive power (and real power) fed to the grid from the RSC independently of the rotational speed of the generator.” ()]; and
d) controlling the DC-to-AC converter of the power conversion system to compensate the stator reactive power and the harmonic [“The line side converter 168 converts the DC power on the DC link 136 into AC output power suitable for the electrical grid 184. In particular, switching elements (e.g. IGBTs) used in bridge circuits of the line side power converter 168 can be modulated to convert the DC power on the DC link 136 into AC power on the line side bus 188. The AC power from the power converter 162 can be combined with the power from the stator of DFIG 120 to provide multi-phase power (e.g. three-phase power) having a frequency maintained substantially at the frequency of the electrical grid 184 (e.g. 50 Hz or 60 Hz).” (col. 8, lines 1-15); wherein “The power converter 162 also compensates or adjusts the frequency of the three-phase power from the rotor for changes, for example, in the wind speed at hub 20 and blades 22. Therefore, mechanical and electrical rotor frequencies are decoupled and the electrical stator and rotor frequency matching is facilitated substantially independently of the mechanical rotor speed.” (col. 8, lines 45-55)].
Gadiraju, however, does not explicitly teach wherein step c) comprises controlling the AC-to-DC converter such that the forced injection of the stator reactive power is maximized at the synchronous speed and decreasing to borders of the predetermined operational speed range.
Sojud, in analogous art, teaches wherein step c) comprises controlling the AC-to-DC converter such that the forced injection of the stator reactive power is maximized at the synchronous speed and decreasing to borders of the predetermined operational speed range [Fig. 18 shows the reactive current capability of DFIG-WT around synchronous speed as a function of active current at nominal voltage. ... At synchronous speed, DPWM and CPWM show more reduction from its maximum value with approximately 12.4% and 19.8%, respectively. Section V. THERMAL MODEL OF MSC on p.741-743].
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 modify the method and system for reactive power control of a wind turbine as disclosed in Gadiraju et al. by applying the known technique of optimizing the reactive current capability of a DFIG-based wind turbine (DFIG-WT) around synchronous speed as a function of active current at nominal voltage, as taught by Sujod et al. Gadiraju already discloses a DFIG wind turbine system employing rotor-side and line-side converters to control reactive power, particularly addressing limitations near synchronous speed. Sujod further teaches that the reactive current capability of a DFIG-WT can be characterized and optimized around synchronous speed, providing detailed analysis and simulation results (see, e.g., Sujod Fig. 18) that guide the allocation of reactive current based on active current levels. Applying Sujod’s approach to the Gadiraju system would have been a straightforward improvement, as both references address the same technical field and problem—maximizing reactive power capability near synchronous speed. The combination would yield the predictable result of enhanced reactive power performance and converter utilization in DFIG wind turbines, using well-understood control and allocation techniques.
Regarding claim 4, Gadiraju/Sujod teaches the method according to claim 1., wherein step c) comprises controlling the AC-to-DC converter such that an AC-voltage is imposed in the rotor windings of the doubly-fed electric machine [“The MSC and LSC are controlled in a dq reference frame. ... The MSC controls active and reactive power of the WT and follows a tracking characteristic to adjust the generator speed for optimal power generation depending on wind speed.” (section II. DFIG-BASED WIND TURBINE on p.737)].
Regarding claim 5, Gadiraju/Sujod teaches the method according to claim 4, wherein the AC-voltage is imposed with a frequency depending on an angle of the electrical grid [“Control of rotor voltage and current enables the generator to remain synchronized with the grid frequency while the wind turbine speed varies (e.g., rotor frequency can differ from the grid frequency).” (col. 1, lines 35-45 on Gadiraju)].
Regarding claim 7, these claim(s) limitations are significantly similar to those of claim(s) 1; and, thus, are rejected on the same grounds.
Regarding claim 9, Gadiraju/Sujod teaches a wind turbine, comprising an upper section on top of a tower, the upper section being pivotable around a vertical yaw axis and having a nacelle and a rotor with rotor blades, the rotor being attached to the nacelle and the rotor blades being rotatable by wind around a horizontal rotor axis, wherein the wind farm comprises the apparatus according to claim 7 [“Fig. 1. Schematic of a DFIG based wind turbine system.” (section II. DFIG-BASED WIND TURBINE on p.737)].
Allowable Subject Matter
Claims 2, 3, 6 and 8 are 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.
Conclusion
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/Ramon A. Mercado/ Supervisory Patent Examiner, Art Unit 3658