General Electric Company v. Vestas Wind Systems A/S

1. Case Identification

• Patent #: 7,102,247
• Filed: April 16, 2018
• Petitioner(s): General Electric Co.
• Patent Owner(s): Vestas Wind Systems A/S
• Challenged Claims: 1-6, 10, and 15

2. Patent Overview

• Title: Circuit Arrangement for a Wind Turbine
• Brief Description: The ’247 patent discloses a circuit arrangement for a variable-speed wind turbine with a double-fed asynchronous generator. The invention is directed at managing grid faults, such as short circuits, by using a switch-controlled resistor to handle rotor overcurrents, allowing the system to temporarily disconnect from and then reconnect to the power grid.

3. Grounds for Unpatentability

Ground 1: Anticipation of Claims 1-4 and 15 by Okamura

• Prior Art Relied Upon: Okamura (Japanese Unexamined Patent Application Publication No. H7-194196).
• Core Argument for this Ground: This ground was presented based on the Patent Owner’s anticipated claim construction, where "temporarily disconnected" means deactivating internal converter switches and the "additional resistor" is located within the converter’s intermediate circuit.
  • Prior Art Mapping: Petitioner argued that Okamura teaches a variable speed power generation system for a wind turbine using a double-fed induction generator. Okamura’s system includes a converter with a chopper circuit (a resistor and a switch) on its DC link. Upon detecting a network fault, Okamura’s controllers suspend the switching operation of the converter’s inverters (i.e., "disconnect" them) and activate the chopper circuit to have the resistor consume the excess rotor current. After the fault subsides, the controllers resume the converter’s operation ("reconnect" it). Petitioner contended this maps directly to the limitations of independent claim 1. Dependent claims 3 (multiple resistors), 4 (two-point regulator), and 15 (regulated resistor on the intermediate circuit) were also argued to be disclosed in Okamura's embodiments and control descriptions.
  • Key Aspects: The entire argument for this ground was predicated on adopting the Patent Owner's expected (and broader) claim interpretations, which Petitioner explicitly disagreed with but used to demonstrate invalidity.

Ground 2: Obviousness of Claims 1-4, 10, and 15 over Okamura in view of Koeppe

• Prior Art Relied Upon: Okamura (Application # H7-194196) and Koeppe (Patent 6,906,434).
• Core Argument for this Ground: This ground asserted that even if Okamura does not explicitly teach actively injecting current after a fault, it would have been obvious to modify Okamura’s system with the teachings of Koeppe.
  • Prior Art Mapping: Koeppe teaches a voltage recovery device that supports a utility network during a fault by injecting reactive power from a capacitive energy storage system via an inverter. Petitioner argued that claim 10’s requirement to supply a capacitive or inductive current (i.e., reactive power) during a short circuit is met by Koeppe.
  • Motivation to Combine: A person of ordinary skill in the art (POSITA) would combine Koeppe's well-known technique for grid support with Okamura's wind turbine system to improve its fault ride-through capability. Petitioner asserted that Okamura's circuit, which already includes a grid-side converter and a DC link capacitor, is the ideal platform for implementing Koeppe’s teachings.
  • Expectation of Success: A POSITA would have had a high expectation of success because it involved applying a known grid-support solution (Koeppe) to a known problem in a compatible system (Okamura) to achieve the predictable result of enhanced grid stability.

Grounds 3 & 4: Obviousness of Claims 5 and 6 over Okamura (and Koeppe) in view of Kumar

• Prior Art Relied Upon: Okamura (Application # H7-194196), Koeppe (Patent 6,906,434), and Kumar (Patent 5,208,741).
• Core Argument for this Ground: This ground argued that the control methods recited in dependent claims 5 and 6 are conventional and would have been obvious additions to the primary prior art combination.
  • Prior Art Mapping: Claim 5 requires controlling the resistor’s switch using pulse-width modulation (PWM) at a fixed frequency. Claim 6 requires using a P, PI, or PID regulator. Kumar was cited as explicitly teaching that chopper circuits (like the one in Okamura) are conventionally controlled using PWM to regulate current. Kumar also explains that such control is part of a closed-loop system for which P, PI, or PID controllers are well-known techniques for achieving an optimal response.
  • Motivation to Combine: A POSITA would be motivated to use the standard control methods taught by Kumar to implement Okamura’s chopper circuit. This would be a simple design choice to achieve finer, more stable, and predictable control over the DC link voltage, representing the application of a known technique to a known device to obtain a predictable result.
  • Expectation of Success: Success would have been expected, as this involves using industry-standard controllers for their intended and well-understood purpose.

4. Key Claim Construction Positions

Petitioner dedicated significant argument to two claim construction disputes, contending its own constructions were correct but presenting its invalidity grounds under the broader interpretations it expected from the Patent Owner in litigation.

• "converter can be at least temporarily disconnected": Petitioner argued the correct construction requires a physical severing of the connection between the converter and the grid. It contended the patent’s specification distinguishes between "disconnecting" and merely "switching off" internal components. However, for the purpose of the IPR, its grounds were based on the Patent Owner's anticipated position that "disconnecting" could mean simply deactivating the converter's internal transistor switches.
• "an additional resistor and a converter": Petitioner argued the "additional resistor" of claim 1 must be external to the "converter" circuit, as suggested by the claim language (the resistor takes over current when the converter is disconnected) and Figures 1 and 3 of the ’247 patent. The grounds, however, were based on the Patent Owner’s anticipated interpretation that the resistor could be internal to the converter circuit, as shown in Figure 5 of the ’247 patent and in the Okamura reference.

5. Arguments Regarding Discretionary Denial

• Petitioner argued that discretionary denial under §325(d) would be inappropriate. Although the Okamura reference was listed in an Information Disclosure Statement during the original prosecution of the ’247 patent, it was a Japanese-language document for which no translation was submitted. Petitioner asserted there was no evidence the Examiner substantively considered Okamura’s specific disclosures, meaning the reference was not "cumulative" to the art considered during prosecution.

6. Relief Requested

• Petitioner requested that the Board institute an inter partes review and find claims 1-6, 10, and 15 of the ’247 patent unpatentable.